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

(cherry picked from commit 51a1d445)

Merged-In: Ia9171fecc9c3ed265b87921b31458de25304486e
Change-Id: I112db6bf0a54dbf7c7e229eb18f29d5034d42e10