output: detect environments less likely to have multibyte characters available

[LawnGnome]

Some environments predate Unicode, and we should avoid using emoji and box drawing characters if we can in those scenarios.

Specifically, we probably want to detect these:

• Really old TERM settings, like vt100.
• Windows Console (but not Windows Terminal), which could look at whether the SESSIONNAME environment variable is Console.

This should be a new field in capabilities that we can then do sensible things with, along with possibly swapping out the standard emoji and spinner variables.