libgui: Add wb_platform_api_improvements flag

This flag will be used for the first set of changes to ConsumerBase and
Surface in support of Camera refactors related to go/warren-buffers.

Bug: 340933794
Flag: EXEMPT adding new flag
Test: n/a
Change-Id: I9e29f03c970967013a67ff6bd22d395ef75d88d8
1 file changed