Create proper coverage multi-module report with AGP 4.2.0

[PaulKlauser]

Include docs on differences and known issues with AGP 7.0.0

Fixes an issue found with including the jacoco task in every module that creates a race and non-deterministic failures of the jacoco task.

The issue with including the task in every module is that when you run ./gradlew jacocoTestReport, all modules will be running their own tests (fine) then their own jacoco task (fine), but each task will be trying to grab all of the exec files for each module.

Sometimes this leads to one module's running of the task trying to read an exec file from another module as that module is writing to it. This fails the task.

Not to mention, this approach will be duplicating the generation of the report, and only the last module to generate the report will technically "own" the report, though each report should be identical.