Add watchOS destination support

[jrcrespoh]

https://github.com/firebase/quickstart-ios/blob/31243d7c5a7a92f4e86e7ac590951cd0a67f845d/scripts/test.sh#L99-L104

[jrcrespoh]

xcodebuild: error: Unable to find a destination matching the provided destination specifier:
		{ platform:iOS Simulator, id:CBDFEF00-6452-4CFF-B8FC-3C3A19EF360F }

	The requested device could not be found because no available devices matched the request.

	Available destinations for the "ABTestingExample (watchOS)" scheme:
		{ platform:iOS Simulator, id:D5CE1612-CFCD-4B7F-A47A-716B710EFAC6, OS:14.5, name:iPhone 11 }
		{ platform:iOS Simulator, id:9A2E88CB-3B04-42F8-B132-BD429A96ECFC, OS:14.5, name:iPhone 11 Pro }
		{ platform:iOS Simulator, id:876FEB8F-5CC6-47E6-B535-BBC169D42B71, OS:14.5, name:iPhone 11 Pro Max }
		{ platform:iOS Simulator, id:CBDFEF00-6452-4CFF-B8FC-3C3A19EF360F, OS:14.5, name:iPhone 12 }
		{ platform:iOS Simulator, id:1D74468B-EEE8-4F2E-9C0B-B2771AAE729C, OS:14.5, name:iPhone 12 Pro }
		{ platform:iOS Simulator, id:3735C965-96A5-4528-91C1-9025D27E67FF, OS:14.5, name:iPhone 12 Pro Max }
		{ platform:iOS Simulator, id:F86F8777-3125-4B30-BF59-E78B3CE01C7C, OS:14.5, name:iPhone 12 mini }

	Ineligible destinations for the "ABTestingExample (watchOS)" scheme:
		{ platform:iOS, id:dvtdevice-DVTiPhonePlaceholder-iphoneos:placeholder, name:Any iOS Device }
		{ platform:watchOS, id:dvtdevice-DVTiOSDevicePlaceholder-watchos:placeholder, name:Any watchOS Device }