feat(live_grep): enable treesitter (closes #2511)

Disabled by default, enable with `_treesitter=true`:
```lua
:FzfLua live_grep _treesitter=true
-- or
:lua FzfLua.live_grep({ _treesitter = true })
```

or permanently via setup under grep:
```lua
require("fzf-lua").setup({
    grep = {
        _treesitter = true,
        -- recommended to use with "--colors match:style:underline"
        rg_opts = "--column --line-number --no-heading --color=always --smart-case "
          .. "--max-columns=4096 --colors match:style:underline -e"
    }
})
```

Author: ibhagwan

lua/fzf-lua/defaults.lua

@@ -786,7 +786,7 @@ M.defaults.grep                  = {
   -- live_grep_glob options
   glob_flag      = "--iglob", -- for case sensitive globs use '--glob'
   glob_separator = "%s%-%-",  -- query separator pattern (lua): ' --'
-  _treesitter    = true,
+  _treesitter    = 1,         -- auto disable in live grep
   _headers       = { "actions", "cwd" },
 }
 

lua/fzf-lua/providers/grep.lua

@@ -60,15 +60,15 @@ M.grep = function(opts)
 end
 
 local function normalize_live_grep_opts(opts)
-  -- disable treesitter as it collides with cmd regex highlighting
-  opts = opts or {}
-  opts._treesitter = false
-  utils.map_set(opts, "winopts.treesitter", nil)
-
   ---@type fzf-lua.config.Grep
   opts = config.normalize_opts(opts, "grep")
   if not opts then return end
 
+  -- auto disable treesitter as it collides with cmd regex highlighting
+  -- ignore if forced with `_treesitter = true` (#2511)
+  local _ts = utils.map_get(opts, "_treesitter")
+  if _ts == 1 then opts = utils.map_set(opts, "winopts.treesitter", false) end
+
   -- we need this for `actions.grep_lgrep`
   opts.__ACT_TO = opts.__ACT_TO or M.grep