Use only 'stableId' to identify Layer/WindowState

The RectsComponent and TreeComponent used to rely on the `id` property
instead of `stableId` to identify elements of type Layer/WIndowState.
This created issues in cases where an element doesn't provide an `id`,
e.g. root layer.

Fix: b/263554032
Test: npm run build:all && npm run test:all
Change-Id: If296baa5402b100f67f5326a065ef569aaf2b842
10 files changed