Adds a patch which creates headers to organize flags added by Ungoogled Chromium
Updates existing patches to use the new headers
Creates flag entries for patches that did not have them previously
Includes "ungoogled-chromium flag" in flag descriptions
Updates the flag documentation
Notes:
`'chrome/android/proviles/afdo.prof'` was removed from `PRUNING_EXCLUDE_PATTERNS`
because it no longer exists.
`core/chromium-upstream/remove-dead-reloc-in-nonalloc-LD-flags.patch` was
dropped as the commit that was backported is part of the Chromium 87 release.
`extra/inox-patchset/0006-modify-default-prefs.patch` now disables third-party
cookies in a similar fashion to GrapheneOS Vanadium.
`extra/debian/disable/device-notifications.patch` was dropped as the changes
that it made have been adopted by Chromium upstream.
