What?

In preparation for the changes proposed in #45982, this PR improves the unit tests for NumberControl:

Why?

The changes in #45982 have the potential to introduces unwanted side effects, and therefore it's better to bolster unit tests in order to gain more confidence when making those changes.

How?

• all tests now run against both the controlled and uncontrolled version of the component

[TODO]:

• test both user input AND setting directly the value programmatically
• add more tests around validation, eg.:
  • test number and string
  • adding non numbers
  • adding numbers outside of range
  • leaving the field empty
  • adding a value, and then deleting it
  • typing and pressing enter
  • typing and blurring the input
  • with and without pressEnterToChange
  • with and without required

Testing Instructions

This PR doesn't introduce runtime changes (the only changes are to the unit tests).

Review the tests code, make sure that all tests pass and expect the correct behaviour.