[ios][platform_view]Use CALayer directly (rather than UIView) as the clip mask #149212
Description
Use case
UIView comes with overhead unrelated to rendering (e.g. hit testing). As experimented in this design doc, there can be non-trivial performance improvement.
Decoupling this from the software rendering work allows us to
(1) measure the improvement separately for a better understanding
(2) land the software rendering PR sooner
Proposal
UIView::mask likely just calls CALayer::mask API. We should directly use CALayer to avoid extra overhead comes with UIView.