SurfaceFlinger: Dump on layer leaks

Every so often some process will leak layer references and
SurfaceFlinger will eventually crash (or refusing to create
new layers because of the max layer count). We never have
enough info to trace these down, and it becomes a horrible
game of chasing repro steps. While we currently have no
complaints about anything like this in T, a recent
12L bug serves as a timely reminder that we should get
this logging in BEFORE the next issue occurs, rather
than after.

Bug: 227286456
Test: Existing tests pass
Change-Id: I2c8b834c93a27204225b482fea1e54837204c9cf