libgui: Add unlimited slot support to Surfaces and Consumers

Surfaces can now use `setMaxDequeuedBufferCount` with any value when the
consumer supports it to give themselves an essentially unlimited number
of buffers to use.

ConsumerBase and its libgui children have been updated to allow for
unlimited buffer slots by default (meaning all users opt into this
automatically), and their implementations have been updated to track the
new variable slot limit.

This is part of go/warren-buffers.

Bug: 341359185
Flag: com.android.graphics.libgui.flags.wb_unlimited_slots
Test: new tests, old tests
Change-Id: I374aa204a2e42a17d95c6e0ffaef2c2caaa9c963