Add a mode to the renderer to substitute *anything* outside of the ASCII space

[estebank]

When encountering some non-printable Unicode characters, we replace them with printable Unicode representations of them. This replacement still relies on Unicode support on the user's terminal. In order to enable use on... less modern systems, added a force_ascii mode to the renderer that replaces anything outside of the ASCII with a replacement string:

error: oops
 --> <current file>:2:8
  |
2 | Second oops <SOH> line
  |        ^^^^ oops

instead of the current

error: oops
 --> <current file>:2:8
  |
2 | Second oops ␁ line
  |        ^^^^ oops

This change unearthed a latent bug where the rendered snippet gets out of sync with the Annotation lo and hi char position, making highlighting spans that had characters replaced with a different number of bytes to be improperly highlighted, as noted in the svg test.

[epage]

Generally, I find it helpful to discuss things first in issues so conversations don't get fragmented and can be found where people expected them. I just noticed we don't have the contrib guide specifically requesting that.

This replacement still relies on Unicode support on the user's terminal. In order to enable use on... less modern systems

Could you provide more context on the end-user concerns that this is addressing? What types of terminals are we talking about? Why is this coming up now?