Add a parent id to the offscreen layer parent proto

We parent all offscreen layers to a fake parent when we generate the proto dump. When generating
the fake parent proto, set a valid parent id of -1 so the flicker test tool does not fail.

Bug: 141326137

Test: flickertest passes
Test: generate winscope trace and check for offscreen layers
Change-Id: I29e0f7bdc736abd8cee58d9a47c08888adcb589d