Add IntDef annotations for transition and animation types.

Add proper @IntDef annotations for mixed transition types and animation
sub-types in DefaultMixedHandler. This provides better type safety
through enum-like constraints for constants and fixes an incorrect value
for ANIM_TYPE_PAIR_TO_PAIR (changed from 1 to 2).

Bug: 387193964
Test: atest WMShellUnitTests
Flag: EXEMPT refactor
Change-Id: Ib78e99c1843052e861b404a516ecb8d4e6705448