`CircularContainer` should have `Masking` set to `true` by default

[jai-x]

Circular edges only seem to show when masking is enabled so it seems like a sensible default?

[smoogipoo]

I believe this was intentional, but really the amount of times you're using a circular container purely for input (not visual) masking purposes are few and between.

[peppy]

The reasoning behind not doing this was a result of a lengthy discussion years back, where we generally came to the consensus that setting default values on a per-container basis is quite a hidden implementation (even if the specifications were sane).

I wouldn't be against this change, but I think if we're going to add more sane defaults we probably, at very least, need a method of documenting them somewhere visible to the consumer.