Fix issue 22776 - string literal printing fails on non-ASCII/non-printable chars

[dkorpel]

The logic of formatting characters is duplicated many times, so I extracted it to a separate function.

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Bugzilla references

Auto-close	Bugzilla	Severity	Description
✓	22776	normal	string literal printing fails on non-ASCII/non-printable chars

Testing this PR locally

If you don't have a local development environment setup, you can use Digger to test this PR:

dub run digger -- build "master + dmd#13662"

[maxhaton]

It might be worth making sure this gets inlined

[dkorpel]

Is this performance critical, and is there a reason to distrust the compiler's judgement on whether to inline this function?