Laziliy initialize SystemActionPerformer

Tests indicate starting up AccessibilityManagerService takes 5ms longer
than expected and may be due to ag/9726764. Unsure how that change
could cause it, but we can take action and avoid initializing
SystemActionPerformer on start up.

Bug: 145909124
Test: builds and registers actions
Change-Id: Id7b8d5bfc450f96691b1810bf701644a0b1ef637