Renamed AUTOFILL_COMPAT_MODE_ALLOWED_PACKAGES.

The syntax of that setting changed from P Developer Preview1 to the final P, so
it's safer to use a new name than risk breaking devices during the update.

Bug: 74458004
Test: atest CtsAutoFillServiceTestCases:VirtualContainerActivityCompatModeTest\
FrameworksCoreTests:SettingsBackupTest

Change-Id: I1c507e8eae20f598dfe259178667ae6c2bc892ff