Fix diagnosis for multi files and deleted file

[LelouchHe]

For includes, the xmake check will check those included files along the way, so the result could be multi-files

And when a file is deleted, the diagnosis should be deleted as well

NOTE: this doesn't parse the includes failure, like when included file doesn't exist, since this failure doesn't specify the file that actually includes the target file, so no way to put it in the right place

[LelouchHe]

btw, i realize that this intellisense could work with Lua-LS addon, as long as we set xmake.lua language to Lua instead of xmake.

This diagnosis focuses on file name xmake.lua, while Lua-LS addon focuses on Lua language.

so setting xmake.lua to Lua gets the better parts of both extensions.