Flutter agent v1.3.5

Improvements and enhancements

• Updated the native Android agent to version 7.8.5. (#254)
• Updated the native iOS agent to version 7.7.10 for Swift Package Manager. CocoaPods installs stay on 7.7.9 because 7.7.10 is not available on CocoaPods. (#254)

Bug fixes

• Stopped recordMetric crashing on iOS when value or units are omitted. (#249)