Revert "Removing flag com.android.window.flags.track_system_ui_context_before_wms from trunk_staging."

This reverts commit 0244c3d61e02643e9f1f3e77d272c12dfc6f37a8.

Reason for revert: This flag is in an inconsistent state. It's turned on everywhere except staging. The flag code is also cleaned up at this point, so this is only a consistency CL that's a no-op.

Bug: 384428048
Change-Id: I172b54569d197f3a8fad41b39ffc5d93dd9aa6fa