feat(HCT): Perform custom migration for HCT when restoring from backup

Sends a broadcast that is picked up by the same receiver in the Settings
app that handles migration for users during OTA.

Bug: 369906140
Test: atest SettingsHelperRestoreTest
Flag: com.android.graphics.hwui.flags.high_contrast_text_small_text_rect
Change-Id: I23ae51da085f9456233e97b15288e55bfd0939c4