Write char::DebugEscape sequences using write_str

[Swatinem]

Instead of writing each char of an escape sequence one by one,
this delegates to Display, which uses write_str internally
in order to write the whole escape sequence at once.

---

This is on top of #124551, and looking at the individual commit, you can see the improvements to the write_calls

[rustbot]

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[Swatinem]

r? @the8472
as you are already reviewing #124551 :-)

[Swatinem]

Even though I’m far from following the best practices for benchmarking, I seem to get quite a consistent improvement from this, even for the benchmarks that are not doing any escaping, possibly because this generates better/smaller code overall?

 name master ns/iter write-str ns/iter diff ns/iter diff % speedup str::debug::ascii_escapes 1,083 1,003 -80 -7.39% x 1.08 str::debug::ascii_only 700 672 -28 -4.00% x 1.04 str::debug::mixed 1,748 1,549 -199 -11.38% x 1.13 str::debug::mostly_unicode 1,250 1,176 -74 -5.92% x 1.06 str::debug::some_unicode 748 717 -31 -4.14% x 1.04 

[bors]

☔ The latest upstream changes (presumably #121150) made this pull request unmergeable. Please resolve the merge conflicts.

[Swatinem]

landed as part of #121150