Add VTS test for clearing buffer slots to Composer HIDL and AIDL

This feature allows SurfaceFlinger to clear buffer slots when buffers
are discarded by SurfaceFlinger clients and will no longer be used,
allowing the graphics memory to be freed immediately.

Bug: 258196272
Test: atest VtsHalGraphicsComposerV2_4TargetTest
Test: atest VtsHalGraphicsComposer3_TargetTest
Change-Id: Ibfbe2078ac419bb8f3880ee3f0512acaad2f5012