fix(lsp): lint warnings, default offset_encoding #24046

- fix lint / analysis warnings
- locations_to_items(): get default offset_encoding from active client
- character_offset(): get default offset_encoding from active client

runtime/lua/vim/lsp/rpc.lua

@@ -36,7 +36,7 @@ end
 local function parse_headers(header)
   assert(type(header) == 'string', 'header must be a string')
   local headers = {}
-  for line in vim.gsplit(header, '\r\n', true) do
+  for line in vim.gsplit(header, '\r\n', { plain = true }) do
     if line == '' then
       break
     end