Since reverting the PR at this point would be a mess I've gone ahead and removed the internals of the container. We should aim to keep the class since it's now part of our public API but it won't work as expected anymore. This is fine for now since we don't actually have anything in it!
- Added a new class `ExtendedContainer` that extends League's container.
- `add` modified to reject classes not in the root Woo namespace.
- Has two new methods, `replace` and `reset_resolved`.
- It's used as the underlying container instead of League's one
in `Container`, but the new methods are not exposed.
- At unit test bootstrap time the globally registered container is
replaced with the extended one that `Container` stores
(grabbed from private property using reflection).
- A new `MockableLegacyProxy` is added. It inherits from `LegacyProxy`
and allows to mock functions, static methods and legacy classes.
- The registeed `LegacyProxy` is replaced with the mockable version
during unit test bootstrap.
- A PHPUnit hook is added to reset the mockable proxy to its initial
state (so that nothing is mocked) before each test.
- `WC_Unit_Test_Case` gets helper methods to mock functions, static
methods and classes without having to retrieve the proxy class.