Add flag com.android.graphics.libgui.flags.allocate_buffer_priority to trunk_staging.

This change was automatically created by advancing the Gantry workflow at:
https://releasetracker.partner.android.com/changes/9pmpcba000001?build_unique_id=android_platform_wear_system_health
Do not edit this file manually or revert this change - use the Gantry workflow to manage the state of this flag.

Bug: 399701430
Flag: com.android.graphics.libgui.flags.allocate_buffer_priority
Ignore-AOSP-First: AConfig change for future AOSP release
Change-Id: I15117576e3d32adc999d31e8c5d7803700af7eac