fix(lsp): use only utf-16 in default client positionEncodings (#23903)

The Nvim client does not yet support multiple offset encodings for
clients in the same buffer. Until it does, stick to utf-16 by default.

runtime/lua/vim/lsp/protocol.lua

@@ -636,9 +636,7 @@ function protocol.make_client_capabilities()
   return {
     general = {
       positionEncodings = {
-        'utf-8',
         'utf-16',
-        'utf-32',
       },
     },
     textDocument = {