Adding 'Patent' to WITH_PERMISSION_ONLY

Ideally we would track these separately but practically they fall into
the same category as the restricted license. It is on the OWNERS and the
reviewers to make sure that they comply with the terms of a Patent file
or any license. Currently we are just generating presubmit warnings that
are being ignored.

This will also enable future tooling that utilises this list for
auditing restricted licenses to surface Patent files.

Bug: 381146326
Change-Id: I0f091bef9649d3a9f7b03940c8634e56bee9541f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/6290872
Reviewed-by: Rachael Newitt <renewitt@google.com>
Commit-Queue: Jordan Brown <rop@google.com>

metadata/fields/custom/license_allowlist.py

@@ -200,6 +200,8 @@ WITH_PERMISSION_ONLY = frozenset([
     "Opus-Patent-BSD-3-Clause",
     "UnRAR",
     # go/keep-sorted end
+    # Patent files are special, and must be handled on a case by case basis.
+    "Patent",
 ])
 
 # These are references to files that are not licenses, but are allowed to be