`lsp-rename`: check if supported before prompting for a name

[nbfalcon]

When I start using a new language sever, I don't know what it supports. If because of that I try to rename something, even though the language server doesn't support it, I just end up wasting my time coming up with a new name.

lsp-rename should do a capability check + prepareRename before asking the user for a new name. This will improve discoverability, because users aren't punished for not knowing that rename doesn't work.

This will be an easy fix.

[kiennq]

Nit: I think via the default key binding and whick-key, the rename option will show up only when the capability is supported

[nbfalcon]

@kiennq users that use M-x or users that have their own custom keybindings won't benefit from that though. We should strive for a consistent, good user-interface where possible.