Central directory instead of per-file _ltex.json

[YodaEmbedding]

Consider how $HOME/.local/state/nvim/undo keeps all swap files in one directory:

$ ls "$HOME/.local/state/nvim/undo"
 %home%mulhaq%test.py
 %home%mulhaq%.cache%nvim%ltex%en-US.txt
 %home%mulhaq%.config%paru%paru.conf
 %mnt%data%code%research%writing%masc-thesis%main.tex
 %mnt%data%code%research%writing%masc-thesis%references%compression.bib
 %mnt%data%code%research%writing%masc-thesis%references%imagecompression.bib
...

Could we do the same for _ltex.json files? For instance:

$ ls "$HOME/.local/state/nvim/ltex/file-local-settings"
 %home%mulhaq%notes.md.ltex.json
 %mnt%data%code%research%writing%masc-thesis%main.tex.ltex.json
 %mnt%data%code%research%writing%masc-thesis%chapters%chapter1.tex.ltex.json
 %mnt%data%code%research%writing%masc-thesis%chapters%chapter2.tex.ltex.json
...

Currently, my directories keep getting cluttered with _ltex.json files!

[YodaEmbedding]

Related: #10