Major refactor of Doom core files

- Remove core-os and move many of its settings out to other core
  libraries, where they belong
- Significantly improve commenting & compartmentalization of many
  settings
- Correct some mis-named public hooks (that were named as if they were
  private)
- Move the vast majority of optimizations to "Optimizations" section in
  core.el
- Don't activate xclip-mode or osx-clipboard-mode if we're accessing
  Emacs through an SSH connection (does more bad than good there)
- Add fast-but-imprecise-scrolling = t
- Set bidi-display-reordering = 'left-to-right, at the recommendation of
  an Emacs dev. Apparently setting it to nil is undefined, as Emacs is
  designed to always assume it's set; setting it explicitly to
  left-to-right will still do what was originally intended by turning it
  off: to reduce line/text scans for bidirectional text, which gives us
  a moderate boost in general runtime snappiness
- Set inhibit-compacting-fon-caches = t on windows (where it struggles
  especially with icon fonts)
- Disables "literal" mode for very large files (because I will be
  backporting so-long.el from Emacs 27 in the next commit)

core/core-lib.el

@@ -1,6 +1,6 @@
 ;;; core-lib.el -*- lexical-binding: t; -*-
 
-(let ((load-path doom-site-load-path))
+(let ((load-path doom--initial-load-path))
   (require 'subr-x)
   (require 'cl-lib))