While we might never be able to have 100% of our code strict, we can at
the very least do it for all of our tests. This ensures that our tests
are using our API with the types as intended by the test author, and not
silently be cast to what our API requires.
* Update PR template
* Trim trailing space
* Support for configuring a Chart Title's overlay
* Provide test coverage for getting/setting a Chart Legend's overlay
Add missing docblock
Because even if it doesn't make a difference in practice, it is
technically more correct to call static methods statically. It
also better advertise that those methods can be used from any context.