Split SCons.Util even more, discourage implicit imports

[Repiteo]

Makes SCons.Util more package-y with a couple of changes:

• Disable type hints for SCons.Util's implicit imports. This keeps the functionality working as-is, but now intellisense and IDEs will discourage not using the correct package explicitly.
• Split tests across the different packages, instead of having everything consolidated in UtilTests.py.

Contributor Checklist:

• I have created a new test or updated the unit tests to cover the new/changed functionality.
• I have updated CHANGES.txt and RELEASE.txt (and read the README.rst).
• I have updated the appropriate documentation

[Repiteo]

Trying to use SCons.Util.sctypes.* here causes circular imports. Could maybe be circumvented with local import syntax, but it's simpler to just use the legacy values and silence the warnings.

[mwichmann]

I don't have a problem with this in concept. Away from big screens for a while, so is kind of hard to review. The new Tests.py files are all moved content, right? (UtilsTests has such a big diff it's collapsing it and not showing, means that'll be hard to tell visually).

[Repiteo]

It's all moved content, correct