feat($locale): Allow currency filter to fall back to maxFrac from locale

- Modify default fallback to `NUMBER_FORMATS.PATTERNS[1].maxFrac`

Note that the default value currently is 2, so it preserves the existing behavior.
can you either use jasmine's mocking library or create a $locale mock for this test instead of trying to reset the value at the end of the test?

reason: if the expectations fail the state won't be restored and that will make all the subsequent tests fail and it will be hard to find the cause.