Feature request: tags support

[ShaolunWang]

Love the plugin! I was wondering would it be possible to have tagfile support in the future? On large codebase lsp may not work properly and tags can be used as a fallback method, especially for c/c++ development.

[hedyhli]

I am generally in favor of this. It could be a separate provider that checks for the tagfile.

However, I don't have much experience with the format of tagfile, so this would have to be implemented by someone with more expertise. PRs welcome!

[underwoodtan]

Universal-ctags support JSON output format, and provided basically enough information, so it's easy to write a simple provider, but ctags don't have the consistency that LSP has, so it's hard to handle conner-cases，and harder to support muti languages。
I have impl a sample systemverilog provider based on ctags. I am not familiar with lua,so it's a bit ugly。Is there someone want to take over it?

i guess it'll be easier to support software language