fix(lsp): remove unnecessary file load/write when renaming (#27621)

Previously rename would unconditionally read the to-be-renamed file from the
disk and write it to the disk. This is redundant in some cases

If the file is not already loaded, it's not attached to lsp client, so nvim
doesn't need to care about this file.
If the file is loaded but has no change, it doesn't need to be written.

runtime/lua/vim/lsp/util.lua

@@ -710,11 +710,12 @@ function M.rename(old_fname, new_fname, opts)
   end
 
   for _, b in ipairs(oldbufs) do
-    vim.fn.bufload(b)
-    -- The there may be pending changes in the buffer
-    api.nvim_buf_call(b, function()
-      vim.cmd('w!')
-    end)
+    -- There may be pending changes in the buffer
+    if api.nvim_buf_is_loaded(b) then
+      api.nvim_buf_call(b, function()
+        vim.cmd('update!')
+      end)
+    end
   end
 
   local newdir = assert(vim.fs.dirname(new_fname))

test/functional/plugin/lsp_spec.lua

@@ -2611,7 +2611,7 @@ describe('LSP', function()
 
       eq(false, exec_lua('return vim.uv.fs_stat(...) ~= nil', old))
       eq(true, exec_lua('return vim.uv.fs_stat(...) ~= nil', new))
-      eq('Old file\n', read_file(new))
+      eq('Old file', read_file(new))
     end)
   end)