feat(tsserver): add _typescript.rename handler

[faergeek]

tsserver calls this method after extracting a variable or function via code action. It enables giving extracted function or variable a name right away without requiring a separate step. Otherwise extracted variable or function is left with a generic name like "newLocal".

[faergeek]

I understand that this is an off-spec handler, though despite that I saw some handlers like eslint/openDoc or similar. The difference might be that eslint code action won't work without eslint/openDoc method at all and _typescript.rename is just for convenience. At the same time this doesn't look like a complicated handler.

[justinmk]

I've discouraged building up features in lspconfig beyond just the minimum needed for basic configuration. We can't maintain hundreds of special handlers for LSP servers, that should be pushed out to specialized plugins.

One thing we should do in lspconfig is establish a pattern for recommending third-party plugins for a given LSP server.

[faergeek]

Fair. I just noticed that some specific handlers were here already and thought may be this one could be added as well.

But leaving it to language-specific plugins makes sense, since it's absence doesn't break anything.

[justinmk]

Fair. I just noticed that some specific handlers were here already and thought may be this one could be added as well.

Yeah. I mean we could add this one too, though it's a slippery slope because we keep getting more. As a typescript user I agree this would be a nice feature.