feat: Add on-device conversion measurement support for iOS

[rencsikmarian]

This PR adds support for Firebase on-device conversion measurement on iOS devices. The feature allows tracking ad conversions using email addresses or phone numbers while maintaining user privacy.

Key changes:

• Added new methods for conversion measurement:
  • initiateOnDeviceConversionMeasurementWithEmail()
  • initiateOnDeviceConversionMeasurementWithPhoneNumber()
  • initiateOnDeviceConversionMeasurementWithHashedEmail()
  • initiateOnDeviceConversionMeasurementWithHashedPhoneNumber()
• Added email normalization and validation
• Added phone number validation (E.164 format)
• Added SHA256 hashing support for secure conversion measurement
• Added GoogleAppMeasurementOnDeviceConversion pod dependency
• Implemented iOS-only functionality with proper error handling for Android

Note: This feature is iOS-only. Android implementations return an appropriate error message.

Usage example:

// Using email
cordova.plugins.firebase.analytics.initiateOnDeviceConversionMeasurementWithEmail("[email protected]")
    .then(() => console.log("Success"))
    .catch(error => console.error(error));

// Using phone number (E.164 format)
cordova.plugins.firebase.analytics.initiateOnDeviceConversionMeasurementWithPhoneNumber("+15555555555")
    .then(() => console.log("Success"))
    .catch(error => console.error(error));

Dependencies:

• Firebase iOS SDK 10.22.0 or later
• GoogleAppMeasurementOnDeviceConversion pod