Add support for RN 0.72 by adding application variants loop

[louiszawadzki]

What and why?

Create an application variants loop if it's missing from the app/build.gradle file. If the android closure is absent, we'll do nothing.

How?

We introduce a state variable to know where we are when we're reading the file line by line.

Review checklist

• [x] Feature or bugfix MUST have appropriate tests (unit)