[ENHANCEMENT] Better "Belt test" implementation

[leptun]

As of now, the function always raises the Z a certain amount. raise_z_above() should be used instead.
Also the LCD rendering could be improved.

Note for later.

[vintagepc]

I'm happy to include this in my open PR on the function.
Is there a suggested layout for the LCD rendering or is that more of a "could be better, not sure how yet"?

[leptun]

The layout is mostly ok. I’m more concerned about the way the screen is rendered.

[vintagepc]

Ah, the custom LCD_belttest_print function that redraws everything? I did think that could be cleaned up. Something more compact/efficient that only updates the relevant display section, correct?

[leptun]

Yep