backport fix(lsp): send didClose, didOpen when languageId changes (#39519)

fix(lsp): send didClose, didOpen when languageId changes

Problem:
If a buffer's filetype changes after the LSP client has already
attached (e.g. from json to jsonc via a modeline), but the client
supports both filetypes, it stays attached. It does not notify the
server of the new languageId, causing the server to incorrectly process
the file using the old languageId.

Solution:
Save the languageId used during textDocument/didOpen, and send
textDocument/didClose + textDocument/didOpen when buffer's languageId
changed.

Lsp spec:
0003fb53f1/_specifications/lsp/3.18/textDocument/didOpen.md (L5)
> If the language id of a document changes, the client
> needs to send a textDocument/didClose to the server followed by a
> textDocument/didOpen with the new language id if the server handles
> the new language id as well.

AI-assisted: Gemini 3.1 Pro

Co-authored-by: phanium <91544758+phanen@users.noreply.github.com>

runtime/lua/vim/_inspector.lua

@@ -30,7 +30,7 @@ local defaults = {
 ---Can also be pretty-printed with `:Inspect!`. [:Inspect!]()
 ---
 ---@since 11
----@param bufnr? integer defaults to the current buffer
+---@param buf? integer defaults to the current buffer
 ---@param row? integer row to inspect, 0-based. Defaults to the row of the current cursor
 ---@param col? integer col to inspect, 0-based. Defaults to the col of the current cursor
 ---@param filter? vim._inspector.Filter Table with key-value pairs to filter the items
@@ -42,27 +42,27 @@ local defaults = {
 ---               - buffer: the buffer used to get the items
 ---               - row: the row used to get the items
 ---               - col: the col used to get the items
-function vim.inspect_pos(bufnr, row, col, filter)
+function vim.inspect_pos(buf, row, col, filter)
   filter = vim.tbl_deep_extend('force', defaults, filter or {})
 
-  bufnr = bufnr or 0
+  buf = buf or 0
   if row == nil or col == nil then
     -- get the row/col from the first window displaying the buffer
-    local win = bufnr == 0 and vim.api.nvim_get_current_win() or vim.fn.bufwinid(bufnr)
+    local win = buf == 0 and vim.api.nvim_get_current_win() or vim.fn.bufwinid(buf)
     if win == -1 then
       error('row/col is required for buffers not visible in a window')
     end
     local cursor = vim.api.nvim_win_get_cursor(win)
     row, col = cursor[1] - 1, cursor[2]
   end
-  bufnr = vim._resolve_bufnr(bufnr)
+  buf = vim._resolve_bufnr(buf)
 
   local results = {
     treesitter = {}, --- @type table[]
     syntax = {}, --- @type table[]
     extmarks = {},
     semantic_tokens = {},
-    buffer = bufnr,
+    buffer = buf,
     row = row,
     col = col,
   }
@@ -79,7 +79,7 @@ function vim.inspect_pos(bufnr, row, col, filter)
 
   -- treesitter
   if filter.treesitter then
-    for _, capture in pairs(vim.treesitter.get_captures_at_pos(bufnr, row, col)) do
+    for _, capture in pairs(vim.treesitter.get_captures_at_pos(buf, row, col)) do
       --- @diagnostic disable-next-line: inject-field
       capture.hl_group = '@' .. capture.capture .. '.' .. capture.lang
       results.treesitter[#results.treesitter + 1] = resolve_hl(capture)
@@ -87,8 +87,8 @@ function vim.inspect_pos(bufnr, row, col, filter)
   end
 
   -- syntax
-  if filter.syntax and vim.api.nvim_buf_is_valid(bufnr) then
-    vim._with({ buf = bufnr }, function()
+  if filter.syntax and vim.api.nvim_buf_is_valid(buf) then
+    vim._with({ buf = buf }, function()
       for _, i1 in ipairs(vim.fn.synstack(row + 1, col + 1)) do
         results.syntax[#results.syntax + 1] =
           resolve_hl({ hl_group = vim.fn.synIDattr(i1, 'name') })
@@ -124,7 +124,7 @@ function vim.inspect_pos(bufnr, row, col, filter)
   end
 
   -- All overlapping extmarks at this position:
-  local extmarks = vim.api.nvim_buf_get_extmarks(bufnr, -1, { row, col }, { row, col }, {
+  local extmarks = vim.api.nvim_buf_get_extmarks(buf, -1, { row, col }, { row, col }, {
     details = true,
     overlap = true,
   })
@@ -159,12 +159,12 @@ end
 ---```
 ---
 ---@since 11
----@param bufnr? integer defaults to the current buffer
+---@param buf? integer defaults to the current buffer
 ---@param row? integer row to inspect, 0-based. Defaults to the row of the current cursor
 ---@param col? integer col to inspect, 0-based. Defaults to the col of the current cursor
 ---@param filter? vim._inspector.Filter
-function vim.show_pos(bufnr, row, col, filter)
-  local items = vim.inspect_pos(bufnr, row, col, filter)
+function vim.show_pos(buf, row, col, filter)
+  local items = vim.inspect_pos(buf, row, col, filter)
 
   local lines = { {} }