LeakCanary should crash in release builds

[pyricau]

Sometimes developers ship LeakCanary in release builds by accident, their users see the LeakCanary icon and get really confused.

We should introduce a new default behavior where if the leakcanary-core-android artifact ships in a non debuggable app, LeakCanary automatically crashes on app startup. This will make it much more likely that the issue is detected early.

The check should rely on InternalAppWatcher.isDebuggableBuild and should be implemented in InternalLeakCanary invoke's function which is invoked on app startup. We should add an XML boolean attribute that allows overriding of this behavior. The exception error message should explain what's happening and mention the boolean XML attribute.

[pyricau]

This is another way to solve what #1793 is trying to solve, at runtime instead of via Lint.