Use commas to separate API exemptions list, not colon.

A colon appears in the type signature of a field, so is not safe to use in
this context.

Test: m
Test: $ adb shell settings put global hidden_api_blacklist_exemptions \
Test: > Landroid/app/Activity;->mResumed:Z,Landroid/view/RemoteAnimationDefinition\\\;

Bug: 73337509
Change-Id: Ia9171fecc9c3ed265b87921b31458de25304486e