break: cleanup preview.treesitter language setting (#1612)

this follows nvim-treesitter more closely but enable can also be a table
of enabled languages

The config now looks like this:
```lua
defaults = {
  preview = {
    treesitter = {
      enable = false,
      -- or
      enable = { "c" },
      -- disable can be set if enable isn't set
      disable = { "perl", "javascript" },
    },
  },
},
```

lua/telescope/config.lua

@@ -593,8 +593,17 @@ append(
                           highlighting, which falls back to regex-based highlighting.
                           `true`: treesitter highlighting for all available filetypes
                           `false`: regex-based highlighting for all filetypes
-                          `table`: table of filetypes for which to attach treesitter
-                          highlighting
+                          `table`: following nvim-treesitters highlighting options:
+                            It contains two keys:
+                              - enable boolean|table: if boolean, enable all ts
+                                                      highlighing with that flag,
+                                                      disable still considered.
+                                                      Containing a list of filetypes,
+                                                      that are enabled, disabled
+                                                      ignored because it doesnt make
+                                                      any sense in this case.
+                              - disable table: containing a list of filetypes
+                                               that are disabled
                           Default: true
       - msg_bg_fillchar:  Character to fill background of unpreviewable buffers with
                           Default: "╱"

lua/telescope/previewers/utils.lua

@@ -82,12 +82,26 @@ end
 utils.highlighter = function(bufnr, ft, opts)
   opts = opts or {}
   opts.preview = opts.preview or {}
-  opts.preview.treesitter = vim.F.if_nil(
-    opts.preview.treesitter,
-    type(conf.preview) == "table" and conf.preview.treesitter
-  )
-  local ts_highlighting = opts.preview.treesitter == true
-    or type(opts.preview.treesitter) == "table" and vim.tbl_contains(opts.preview.treesitter, ft)
+  opts.preview.treesitter = vim.F.if_nil(opts.preview.treesitter, conf.preview.treesitter)
+  if type(opts.preview.treesitter) == "boolean" then
+    local temp = { enable = opts.preview.treesitter }
+    opts.preview.treesitter = temp
+  end
+
+  local ts_highlighting = (function()
+    if type(opts.preview.treesitter.enable) == "table" then
+      if vim.tbl_contains(opts.preview.treesitter.enable, ft) then
+        return true
+      end
+      return false
+    end
+
+    if vim.tbl_contains(vim.F.if_nil(opts.preview.treesitter.disable, {}), ft) then
+      return false
+    end
+
+    return opts.preview.treesitter.enable == nil or opts.preview.treesitter.enable == true
+  end)()
 
   local ts_success
   if ts_highlighting then