Measure and report test coverage of "logins" component

[rfk]

I started an experiment on this here but it reports a depressingly low 25% coverage. Much of the missing coverage comes from integration tests, or tests that exercise the Kotlin and Swift bindings. So this issue tracks generating a coverage report that takes all of that into account.

┆Issue is synchronized with this Jira Task

[rfk]

We should also take a look at reporting coverage of the Kotlin and Swift code.

[cse-test-sync]

➤ Janet Dragojevic commented:

According to [~tchiovoloni@mozilla.com] FF for IOS repo has some tests.  Most tests are in the logins repository are more like "smoke tests" and are not as good as the android test coverage. However ios specific functionality is small.

[rfk]

There are some notes on how glean does their code-coverage here: https://mozilla.github.io/glean/book/code_coverage.html#generating-rust-reports-locally

[thomcc]

@Dexterp37, @badboy Have y'all had any success for generating coverage reports that include code called over the FFI, e.g. from android code? AFAICT that doesn't include that, but maybe I'm misreading.

[badboy]

Nope, we're pretty much only doing code coverage per language.