docs(lsp): annotate with vim.lsp.protocol.Methods enum #29521

Added the enum type annotation `vim.lsp.protocol.Methods` to provide some intellisense support.

scripts/gen_lsp.lua

@@ -60,9 +60,10 @@ end
 local function gen_methods(protocol)
   local output = {
     '-- Generated by gen_lsp.lua, keep at end of file.',
-    '--- LSP method names.',
     '---',
+    '---@enum vim.lsp.protocol.Methods',
     '---@see https://microsoft.github.io/language-server-protocol/specification/#metaModel',
+    '--- LSP method names.',
     'protocol.Methods = {',
   }
   local indent = (' '):rep(2)