patch_sync: Fix PatchDictSchema fields

These were out of alphabetical order, and serde_json would write
them in the incorrect order to the PATCHES.json file.

Additionally, the `platforms` field may end up
being null after some discussion with the Android team.

This converts platforms to an Optional accordingly.

BUG=b:209493133
TEST=patch_sync transpose <...>

Change-Id: I7c0b2e984d713698a0ed53e7f36b38bef1a49d1c
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/toolchain-utils/+/3379480
Reviewed-by: George Burgess <gbiv@chromium.org>
Tested-by: Jordan Abrahams-Whitehead <ajordanr@google.com>
Commit-Queue: Jordan Abrahams-Whitehead <ajordanr@google.com>
1 file changed