For some reason, prior to this fix, the boolean set matching
code (within `animation_transition_expr.ts`) failed to remain
the same when compiled with closure. This refactor makes sure
that the code stays in tact.
Reproduction Details:
Passes without `ng build --prod`: https://burger.stackblitz.io/
Fails with `ng build --prod`: http://burger.fxck.cz/Closes#20374
PR Close#20725