feat(metrics): Add BeforeEmitMetrics callback #7596

Job	Run time
UI Tests for ios_objc on Simulators	5m 47s
iOS-Swift UI Tests iPhone 8 (13.7)	9m 44s
UI Tests for tvos_swift on Simulators	3m 15s
iOS-Swift UI Tests iPhone 8 (15.5)	7m 16s
iOS-Swift UI Tests iPhone 14 (16.4)	10m 24s
UI Tests with Address Sanitizer	14m 36s
iOS-Swift UI Tests iPhone 15 (17.2)	19m 26s
UI Tests for SwiftUI on iPhone 8 (15.2) Simulator	4m 20s
UI Tests for SwiftUI on iPhone 8 (16.1) Simulator	4m 58s
	1h 19m 46s

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