Resize balance label font size based on content width in Payment Request View

[tanx]

In order for the Balance number to resize correctly we should add support to react-native-web for adjustsFontSizeToFit. I created an issue upstream: necolas/react-native-web#889

[valentinewallace]

@tanx Just to be sure, this issue is for making a PR to react-native-web, right?

[tanx]

@tanx Just to be sure, this issue is for making a PR to react-native-web, right?

@valentinewallace sorry for the late reply on this. Ideally the solution would be the same as #879