fix(lsp): when prefix is non word add all result into matches (#30044)

Problem: prefix can be a symbol like period, the fuzzy matching can't
handle it correctly.

Solution: when prefix is empty or a symbol add all lsp completion
result into matches.

runtime/lua/vim/lsp/completion.lua

@@ -238,7 +238,7 @@ function M._lsp_to_complete_items(result, prefix, client_id)
 
   ---@type fun(item: lsp.CompletionItem):boolean
   local matches
-  if prefix == '' then
+  if not prefix:find('%w') then
     matches = function(_)
       return true
     end