Add EuiccManager#retainSubscriptionsOnFactoryReset API.

By default, all subscriptions are wiped on first boot after a factory
reset. This ensures that if data is wiped outside of userspace (e.g.
in fastboot/recovery), the profiles are wiped, as there's no way to
offer this option to users in those modes - the radio isn't available
for us to access the eUICC.

This API provides a way to bypass this wipe if the user opts to retain
the policies for a wipe done from userspace (e.g. by unchecking the
"Wipe eUICC" checkbox in platform settings before wiping). We tell the
LPA to note this and skip the wipe on the ensuing factory reset.

Change-Id: I2fe472417497e28b043841a5aa2dc9efa45ebbff
Test: TreeHugger
Fixes: 62681577