Fix for latin1 issue

[Hydrocharged]

This potentially fixes:

• Error importing mysqldump with incorrect string value dolt#8580

There's a longer comment in the code itself, but the summary is that this is a character set conversion issue. Perhaps it's repertoires or something else, but hopefully this moves us closer to the logically correct behavior.

[max-hoffman]

LGTM, two comments would be (1) hypothetically if this wasn't the fix, is there a way to improve the error message so we would have more info next time? (2) is perf OK for the default encodings? strings are already expensive so it would be nice if encodings.StringToBytes(val) avoided doing extra work when unnecessary. If there are perf issues, maybe only do the conversion and recheck if it fails the first time?

[Hydrocharged]

I'll make a new PR to adjust the error message. We can definitely provide a better one. encodings.StringToBytes(val) is the more performant alternative to just []byte{val) since it's getting the internal slice using the unsafe package, so there would technically be a minor performance uplift from using it.