module!: add :editor whitespace

BREAKING CHANGE: Moves ws-butler, dtrt-indent, and whitespace defaults
out of Doom's core and into a new module. ws-butler is gated behind
+trim and dtrt-indent behind +guess. Users who depend on/like these
packages will need to enable the new module and their respective
flags (which is the default going forward).

This change is motivated by an ongoing effort to slim down Doom's
core (by (re)moving non-essentials from it).

This also addresses an issue where dtrt-indent would vastly increase
load times for some major-modes (e.g. elixir-mode & elm-mode, see #7537)
by restricting it to non-project files and non-read-only buffers AND
excludign those two major modes from indent guessing.

Fix: #8516
Fix: #7537

lisp/doom-ui.el

@@ -502,17 +502,6 @@ windows, switch to `doom-fallback-buffer'. Otherwise, delegate to original
         show-paren-when-point-in-periphery t))
 
 
-;;;###package whitespace
-(setq whitespace-line-column nil
-      whitespace-style
-      '(face indentation tabs tab-mark spaces space-mark newline newline-mark
-        trailing lines-tail)
-      whitespace-display-mappings
-      '((tab-mark ?\t [?› ?\t])
-        (newline-mark ?\n [?¬ ?\n])
-        (space-mark ?\  [?·] [?.])))
-
-
 ;;
 ;;; Third party packages
 
@@ -768,12 +757,5 @@ triggering hooks during startup."
   (put sym 'disabled "Doom doesn't support `customize', configure Emacs from $DOOMDIR/config.el instead"))
 (put 'customize-themes 'disabled "Set `doom-theme' or use `load-theme' in $DOOMDIR/config.el instead")
 
-(after! whitespace
-  (defun doom--in-parent-frame-p ()
-    "`whitespace-mode' inundates child frames with whitespace markers, so
-disable it to fix all that visual noise."
-    (null (frame-parameter nil 'parent-frame)))
-  (add-function :before-while whitespace-enable-predicate #'doom--in-parent-frame-p))
-
 (provide 'doom-ui)
 ;;; doom-ui.el ends here