Implement Mask

[marlenecota]

Feature Request

https://github.com/react-native-svg/react-native-svg#mask
https://developer.mozilla.org/en-US/docs/Web/SVG/Element/mask

Possible implementation

• Add new map to SvgView -> m_masks
• Override Render to no-op.
• I think it's similar to ClipPath in using CreateLayer(opacity, clipGeometry), but then also applying AlphaMaskEffect.