Should scrolling/printing out-of-range characters on the display be an "error glyph"

[microbit-carlos]

This might be considered a breaking change, and so, we might not want to change this.

The issue is that when trying to scroll or print UTF-8 long characters, like 갎, we end up with 3 empty characters (UTF-8 encoding is 0xEAB08E), which might make it look like the screen animation has ended.

• Related to: For characters not in the font, display scrolls a null pointer #423
• Related to: Should the display be cleared when trying to print an invalid character? #424

Having an "error character" instead of a white space means that at least it shows something unexpected but a bit more obvious, that doesn't resemble a latin letter.
My first thought would be that people might already be used to see squares ▯ or the replacement character � .

[microbit-carlos]

@JohnVidler suggested we could also have this a config option with space by default.

[microbit-carlos]

Some discussion about a possible implementation if we decide to do this:

• Display scroll an empty char if the requested char is out-of-range.  codal-core#168 (comment)