infra: Add binary-size bots for android-desktop

Similar to the current android size checker builders, this adds some
builders for android-desktop:
- CI generators for arm64 and x64
- optional trybots for arm64 and x64

There's no plan to add these to the CQ. Will keep them optional for
now; but we can consider promoting them if there are many size
regression on desktop.

The builder's recipe may not be compatible with android-desktop and/or
x64, so these may be broke out of the gate. Will fix in follow-ups if
that's the case. These won't close the tree or alert gardeners until
then.

Machines for these builders are being added in
https://crrev.com/i/8549580.

Bug: 420639761
Change-Id: Ia4755a7bd1c3df4645bb87b3b71733ef1b0efc8f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6892028
Commit-Queue: Ben Pastene <bpastene@chromium.org>
Reviewed-by: Haiyang Pan <hypan@google.com>
Cr-Commit-Position: refs/heads/main@{#1508520}