Add keymap descriptions

[SimonLammer]

This is very useful for integration with which-key. By default, which-key would describe a mapping with the function call - e.g. require("trouble").action("open_vsplit"), which is not too bad to read, but often truncated to e.g. require("trouble").action("op. With this patch, the which-key description reads Trouble open_vsplit instead.

Before:

                 $ ➜ End of line                               <C-K> ➜ Switch Window up                              b ➜ Previous word                                 m ➜ require("trouble").action("to …               > ➜ +Indent right
                 % ➜ Matching character: '()', '{} …           <C-L> ➜ Switch Window right                           e ➜ Next end of word                              o ➜ require("trouble").action("ju …               [ ➜ +Previous...
                 & ➜ Nvim builtin                              <C-N> ➜ Nvimtree Toggle window                        F ➜ Move to previous char                         P ➜ require("trouble").action("to …               ] ➜ +Next...
                 0 ➜ Start of line                             <C-S> ➜ File Save                                     f ➜ Move to next char                             p ➜ require("trouble").action("pr …           <c-w> ➜ +window
                 ; ➜ CMD enter command mode                    <C-T> ➜ require("trouble").action("op …               G ➜ Last line                                     q ➜ require("trouble").action("cl …        <leader> ➜ +prefix
                 ? ➜ require("trouble").action("he …           <C-V> ➜ require("trouble").action("op …               H ➜ Home line of window (top)                     r ➜ require("trouble").action("re …               c ➜ +Change
                 ^ ➜ Start of line (non-blank)                 <C-X> ➜ require("trouble").action("op …               h ➜ Left                                          s ➜ require("trouble").action("sw …               d ➜ +Delete
                 { ➜ Previous empty line                        <CR> ➜ require("trouble").action("ju …               j ➜ Down                                          t ➜ Move before next char                         g ➜ +Goto...
                 } ➜ Next empty line                           <M-h> ➜ Terminal New horizontal term                  k ➜ Up                                            T ➜ Move before previous char                     v ➜ +Visual Character Mode
     <2-LeftMouse> ➜ require("trouble").action("ju …           <M-i> ➜ Terminal Toggle Floating term                 K ➜ require("trouble").action("ho …               w ➜ Next word                                     y ➜ +Yank (copy)
             <C-C> ➜ File Copy whole                           <M-v> ➜ Terminal Toggleable vertical  …               l ➜ Right                                         Y ➜ Nvim builtin                                  z ➜ +Fold
             <C-H> ➜ Switch Window left                      <S-Tab> ➜ Buffer Goto prev                              L ➜ Last line of window                           ! ➜ +Filter through external prog …
             <C-J> ➜ Switch Window down                        <Tab> ➜ Buffer Goto next                              M ➜ Middle line of window                         < ➜ +Indent left

After:

                 $ ➜ End of line                               <C-K> ➜ Switch Window up                              b ➜ Previous word                                 m ➜ Trouble toggle_mode                           > ➜ +Indent right
                 % ➜ Matching character: '()', '{} …           <C-L> ➜ Switch Window right                           e ➜ Next end of word                              o ➜ Trouble jump_close                            [ ➜ +Previous...
                 & ➜ Nvim builtin                              <C-N> ➜ Nvimtree Toggle window                        f ➜ Move to next char                             p ➜ Trouble preview                               ] ➜ +Next...
                 0 ➜ Start of line                             <C-S> ➜ File Save                                     F ➜ Move to previous char                         P ➜ Trouble toggle_preview                    <c-w> ➜ +window
                 ; ➜ CMD enter command mode                    <C-T> ➜ Trouble open_tab                              G ➜ Last line                                     q ➜ Trouble close                          <leader> ➜ +prefix
                 ? ➜ Trouble help                              <C-V> ➜ Trouble open_vsplit                           h ➜ Left                                          r ➜ Trouble refresh                               c ➜ +Change
                 ^ ➜ Start of line (non-blank)                 <C-X> ➜ Trouble open_split                            H ➜ Home line of window (top)                     s ➜ Trouble switch_severity                       d ➜ +Delete
                 { ➜ Previous empty line                        <CR> ➜ Trouble jump                                  j ➜ Down                                          t ➜ Move before next char                         g ➜ +Goto...
                 } ➜ Next empty line                           <M-h> ➜ Terminal New horizontal term                  K ➜ Trouble hover                                 T ➜ Move before previous char                     v ➜ +Visual Character Mode
     <2-LeftMouse> ➜ Trouble jump                              <M-i> ➜ Terminal Toggle Floating term                 k ➜ Up                                            w ➜ Next word                                     y ➜ +Yank (copy)
             <C-C> ➜ File Copy whole                           <M-v> ➜ Terminal Toggleable vertical  …               l ➜ Right                                         Y ➜ Nvim builtin                                  z ➜ +Fold
             <C-H> ➜ Switch Window left                      <S-Tab> ➜ Buffer Goto prev                              L ➜ Last line of window                           ! ➜ +Filter through external prog …
             <C-J> ➜ Switch Window down                        <Tab> ➜ Trouble jump                                  M ➜ Middle line of window                         < ➜ +Indent left

[folke]

Development on the main branch is EOL.

Trouble has been rewritten and will be merged in main soon.

This feature has been implemented.

For more info, see https://github.com/folke/trouble.nvim/tree/dev