Simplify MakePrintable by using AND and avoiding converting to string

[pavkam]

This PR simplifies MakePrintable by using simpler bitwise OR instead of string manipulation.

Pull Request checklist:

• I've named my PR in the form of "Fixes #issue. Terse description."
• My code follows the style guidelines of Terminal.Gui - if you use Visual Studio, hit CTRL-K-D to automatically reformat your files before committing.
• My code follows the Terminal.Gui library design guidelines
• I ran dotnet test before commit
• I have made corresponding changes to the API documentation (using /// style comments)
• My changes generate no new warnings
• I have checked my code and corrected any poor grammar or misspellings
• I conducted basic QA to assure all features are working

[tig]

Can you please provide a unit test that helps ensure this won't cause a regression?

I really appreciate your attention to detail and am excited to have you helping!

[pavkam]

@tig -- added two parameterized tests

[tig]

Before I accept this, I'd like confirmation that this change has been thoroughly tested on Windows, Linux, and the Mac.

I don't fully understand the code paths/scenarios involved where this method is used and am nervous about introducing a regression in an area where we have really poor unit testing (all drivers).

[pavkam]

Before I accept this, I'd like confirmation that this change has been thoroughly tested on Windows, Linux, and the Mac.

I don't fully understand the code paths/scenarios involved where this method is used and am nervous about introducing a regression in an area where we have really poor unit testing (all drivers).

It's a straightforward method. Unit tests cover all scenarios that would be there.

I don't think deeper testing is needed for this particular change.

[BDisp]

Before I accept this, I'd like confirmation that this change has been thoroughly tested on Windows, Linux, and the Mac.

I don't fully understand the code paths/scenarios involved where this method is used and am nervous about introducing a regression in an area where we have really poor unit testing (all drivers).

I confirm that the method is common for all drivers and this is a short way to get the hexadecimal from the rune which is well written. Thanks @pavkam.