Rebind RET rather than remapping newline

The remapping was global, preventing its use in insert mode anywhere.
Binding to RET is less destructive.

modules/config/default/+bindings.el

@@ -15,7 +15,7 @@
       :nmvo doom-localleader-key nil
 
       ;; Swap RET/C-j in insert mode
-      :i [remap newline] #'newline-and-indent
+      :gi "RET" #'newline-and-indent
       :i  "C-j" #'+default/newline
 
       ;; --- Global keybindings ---------------------------