feat(extmarks,ts,spell): full support for spelling

- Added 'spell' option to extmarks:

  Extmarks with this set will have the region spellchecked.

- Added 'noplainbuffer' option to 'spelloptions':

  This is used to tell Neovim not to spellcheck the buffer. The old
  behaviour was to spell check the whole buffer unless :syntax was set.

- Added spelling support to the treesitter highlighter:

  @spell captures in highlights.scm are used to define regions which
  should be spell checked.

- Added support for navigating spell errors for extmarks:

  Works for both ephemeral and static extmarks

- Added '_on_spell_nav' callback for decoration providers:

  Since ephemeral callbacks are only drawn for the visible screen,
  providers must implement this callback to instruct Neovim which
  regions in the buffer need can be spell checked.

  The callback takes a start position and an end position.

  Note: this callback is subject to change hence the _ prefix.

- Added spell captures for built-in support languages

Co-authored-by: Lewis Russell <lewis6991@gmail.com>
Co-authored-by: Björn Linse <bjorn.linse@gmail.com>

runtime/lua/vim/treesitter/highlighter.lua

@@ -97,6 +97,7 @@ function TSHighlighter.new(tree, opts)
   if vim.g.syntax_on ~= 1 then
     vim.api.nvim_command('runtime! syntax/synload.vim')
   end
+  vim.bo[self.bufnr].spelloptions = 'noplainbuffer'
 
   self.tree:parse()
 
@@ -156,7 +157,7 @@ function TSHighlighter:get_query(lang)
 end
 
 ---@private
-local function on_line_impl(self, buf, line)
+local function on_line_impl(self, buf, line, spell)
   self.tree:for_each_tree(function(tstree, tree)
     if not tstree then
       return
@@ -193,7 +194,9 @@ local function on_line_impl(self, buf, line)
       local start_row, start_col, end_row, end_col = node:range()
       local hl = highlighter_query.hl_cache[capture]
 
-      if hl and end_row >= line then
+      local is_spell = highlighter_query:query().captures[capture] == 'spell'
+
+      if hl and end_row >= line and (not spell or is_spell) then
         a.nvim_buf_set_extmark(buf, ns, start_row, start_col, {
           end_line = end_row,
           end_col = end_col,
@@ -201,6 +204,7 @@ local function on_line_impl(self, buf, line)
           ephemeral = true,
           priority = tonumber(metadata.priority) or 100, -- Low but leaves room below
           conceal = metadata.conceal,
+          spell = is_spell,
         })
       end
       if start_row > line then
@@ -217,7 +221,21 @@ function TSHighlighter._on_line(_, _win, buf, line, _)
     return
   end
 
-  on_line_impl(self, buf, line)
+  on_line_impl(self, buf, line, false)
+end
+
+---@private
+function TSHighlighter._on_spell_nav(_, _, buf, srow, _, erow, _)
+  local self = TSHighlighter.active[buf]
+  if not self then
+    return
+  end
+
+  self:reset_highlight_state()
+
+  for row = srow, erow do
+    on_line_impl(self, buf, row, true)
+  end
 end
 
 ---@private
@@ -244,6 +262,7 @@ a.nvim_set_decoration_provider(ns, {
   on_buf = TSHighlighter._on_buf,
   on_win = TSHighlighter._on_win,
   on_line = TSHighlighter._on_line,
+  _on_spell_nav = TSHighlighter._on_spell_nav,
 })
 
 return TSHighlighter