The Effect Controls tab gets the lock icon the Composition viewers and the
Timeline have (panel.tab.EffectControls.lock). Locked, the panel and its
tab name keep the layer they showed while that layer's comp is active,
whatever is selected next, so a pick whip from another layer's property
can reach its parameters. An effect dropped on the locked panel goes to
its layer and leaves the selection alone; one applied to another layer
says the panel is locked. Deleting the layer or its comp, or replacing
the project, unlocks the panel, which follows the selection again. The
lock is UI state (UiState::effect_controls_lock) and agents set it with
ui.set {effectControlsLocked}.
Fixes#3193
vangel76
f3a9afda14