Check language server rename support before showing rename-to prompt

[the-mikedavis]

If a language server doesn't support LSP renaming, rename_symbol (<space>r) should bail early. Currently it creates the "rename-to" prompt and then fails to rename.

We check whether the server declares rename support here when creating the rename request future:

helix/helix-lsp/src/client.rs

Lines 1115 to 1120 in d63e570

	// Return early if the language server does not support renaming.
	match capabilities.rename_provider {
	Some(lsp::OneOf::Left(true)) | Some(lsp::OneOf::Right(_)) => (),
	// None | Some(false)
	_ => return None,
	};

(The rename text entered in the prompt is used in the params for that request.) We should extract that match as a function:

pub fn supports_rename(&self) -> bool { /* check rename capability */ }

and then check that support before creating the prompt.

bash-language-server is a language server in the wild that doesn't support symbol renaming and can be used to test this.