refactor: deprecate EMACS2[89]+, NATIVECOMP, MODULES

To reduce redundancy, remove the maintenance hassle that version
constants would impose later on, and rely on built-in
facilities (featurep) more over global variables or doomisms, these
global constants have been deprecated in favor of Emacs "features":

- EMACS28+   -- replace with (> emacs-major-version 27)
- EMACS29+   -- replace with (> emacs-major-version 28)
- NATIVECOMP -- replace with (featurep 'native-compile)
- MODULES    -- replace with (featurep 'dynamic-modules)

(These constants will be formally removed when v3 is released. The IS-*
constants are likely next, but I haven't decided on their substitutes
yet)

I also decided to follow native-compile's example and provide features
for Emacs' system features (since system-configuration-features' docs
outs itself as a poor method to detect features):

- dynamic-modules
- jansson
- native-compile -- this one already exists, but will instead be removed
  if it's non-functional; i.e. (native-comp-available-p) returns nil.

These are now detectable using featurep, which is fast and built-in.

modules/editor/evil/config.el

@@ -53,7 +53,7 @@ directives. By default, this only recognizes C directives.")
         evil-undo-system
         (cond ((featurep! :emacs undo +tree) 'undo-tree)
               ((featurep! :emacs undo) 'undo-fu)
-              (EMACS28+ 'undo-redo)))
+              ((> emacs-major-version 27) 'undo-redo)))
 
   ;; Slow this down from 0.02 to prevent blocking in large or folded buffers
   ;; like magit while incrementally highlighting matches.

modules/editor/evil/init.el

@@ -136,7 +136,7 @@ variable for an explanation of the defaults (in comments). See
       elisp-slime-nav
       embark
       emms
-      ,@(when EMACS29+ '(emoji))
+      ,@(if (> emacs-major-version 28) '(emoji))
       epa
       ert
       eshell
@@ -226,7 +226,7 @@ variable for an explanation of the defaults (in comments). See
       scroll-lock
       selectrum
       sh-script
-      ,@(when EMACS28+ '(shortdoc))
+      ,@(if (> emacs-major-version 27) '(shortdoc))
       simple
       simple-mpc
       slime

modules/emacs/vc/autoload/bug-reference-backport.el

@@ -1,5 +1,5 @@
 ;;; emacs/vc/autoload/bug-reference-backport.el -*- lexical-binding: t; -*-
-;;;###if (not EMACS28+)
+;;;###if (< emacs-major-version 28)
 ;; DEPRECATED Remove when Emacs 27.x support is dropped
 
 ;; In Emacs 28, the built-in bug-reference package started consulting vc for

modules/term/eshell/autoload/backport.el

@@ -1,5 +1,5 @@
 ;;; term/eshell/autoload/mode.el -*- lexical-binding: t; -*-
-;;;###if (not EMACS28+)
+;;;###if (< emacs-major-version 28)
 
 ;; DEPRECATED Remove this when we drop Emacs 27 support.
 

modules/term/vterm/config.el

@@ -1,7 +1,7 @@
 ;;; term/vterm/config.el -*- lexical-binding: t; -*-
 
 (use-package! vterm
-  :when (bound-and-true-p module-file-suffix)
+  :when (featurep 'dynamic-modules)
   :commands vterm-mode
   :hook (vterm-mode . doom-mark-buffer-as-real-h)
   :hook (vterm-mode . hide-mode-line-mode) ; modeline serves no purpose in vterm

modules/ui/ligatures/config.el

@@ -179,7 +179,7 @@ and cannot run in."
 
  ;; Harfbuzz and Mac builds do not need font-specific ligature support
  ;; if they are above emacs-27.
- ((and EMACS28+
+ ((and (> emacs-major-version 27)
        (or (featurep 'ns)
            (string-match-p "HARFBUZZ" system-configuration-features))
        (featurep 'composite))  ; Emacs loads `composite' at startup