fix: borderRadius outline and border drawable fixes

[janicduplessis]

Summary

Two issues when animating borderRadius alongside other properties:

1. Android: elevation shadow ignores style borderRadius. The custom ViewOutlineProvider set in init always read _borderRadius (the animated value, 0 when not animated). Elevation shadows rendered with square corners even when style={{ borderRadius: 16 }} was set. Fix: only use the custom provider when MASK_BORDER_RADIUS is in the bitmask; otherwise fall back to ViewOutlineProvider.BACKGROUND which reads the corner radius from the background drawable.

2. Android: borders don't follow animated borderRadius. setAnimateBorderRadius updated the outline but not the BorderDrawable, so borders rendered with square corners during radius animations. Fix: also call BackgroundStyleApplicator.setBorderRadius each frame to sync the border drawable.

3. iOS: masksToBounds clips shadows. We were setting masksToBounds = YES whenever borderRadius > 0, which clips content outside bounds — including shadows. Since RN defaults to overflow: visible, this was incorrect. Fix: stop setting masksToBounds entirely; cornerRadius alone handles visual rounding. Users can control clipping via style={{ overflow: 'hidden' }}.

Test Plan

• yarn format:write && yarn lint && yarn test — all 65 tests pass.
• Verify on iOS: animated borderRadius + shadow props render correctly (shadow not clipped).
• Verify on Android: animated borderRadius + borderWidth render with matching rounded corners. elevation with style borderRadius shows correct shadow shape.