ZegoEffectsFaceDetectionResult constructor Null safety

1. zego_effects_plugin
2. zego_effects_defines
3. ZegoEffectsFaceDetectionResult
4. ZegoEffectsFaceDetectionResult constructor

ZegoEffectsFaceDetectionResult class

1. Constructors
2. ZegoEffectsFaceDetectionResult
3. Properties
4. point
5. score
6. size