Allow vars_ and func_ in code actions to be configured

[karthiknadig]

Currently code action provides random function and variable names when extracting. We want to use set it a constant value like new_var, or new_func, and let the users change the name as needed.

/cc @luabud

[pappasam]

I don't believe this was possible in LSP 3.15, but it might be possible in LSP 3.16 with codeAction/resolve. That said, once again, the same 2 issues:

1. My client (coc) doesn't yet support 3.16, so this will be hard for me to test in practice until the relevant PR is resolved
2. (bigger issue) pygls doesn't yet support 3.16

I'm happy to keep this issue, and any other 3.16-related issues, open. We can flag them with a LSP-3.16 label or something to stay organized

[pappasam]

I'd be happy to consider any suggestions you may have here. I've considered this in the past, but specifying data for codeAction is not very straightforward. For example, "inline variable" doesn't need a new name, but "extract into variable" does. Additionally, because the LSP spec crams all code actions into LSP request / response, differences between code actions become really hard to handle without editor-specific logic

[dimbleby]

microsoft/language-server-protocol#764, and microsoft/language-server-protocol#1164

So far as I can see the TLDR is that the protocol just doesn't support this yet, not even at 3.16.

(codeAction/resolve seems like it would be a good opportunity to provide a new name, having chosen the refactoring, but I don't think that's what it currently is for)

[karthiknadig]

@pappasam I was thinking of using initializationOptions for this. We wanted to use a constant value in this case instead of the randomly generated names.