Remove Locale.setDefault

Remove all calls to Locale.setDefault in tests and production code.

That function does not operate on the current thread; it affects all threads in the JVM. As such, it may affect other tests running at the same time, and affect other statements running at the same time.

I hope, and believe, that the production code does not depend on Locale.getDefault. But let's make sure by removing setDefault from all tests.

Add Locale.setDefault to forbidden-apis.