Merge "Add FLAG_IMMUTABLE to PendingIntent in LegacyModeSmsHandler." into pi-dev am: 44b02956c4

Original change: https://googleplex-android-review.googlesource.com/c/platform/packages/apps/Dialer/+/16199731

Change-Id: Ic9d83df587f3de366c88cbc01978c859fc4155b7