x/tools/gopls: rename: handle generic methods more precisely

[adonovan]

gopls's renaming is tricky in the presence of generic methods, and our support for them is rudimentary. The challenge is in trying to decide which interfaces and methods correspond (and must be renamed together) when type parameters are involved. Recent changes to the renaming implementation for incrementalized type checking have not made things worse but have made us more aware of the problems and the paucity of testing generally. We should try to come up with a more comprehensive theory of how to do it. This isn't a regression so it needn't happen for v0.12.0.

[gopherbot]

Change https://go.dev/cl/464902 mentions this issue: gopls/internal/lsp/source/rename: incremental renaming