Rollup merge of #124551 - Swatinem:debug-str-bench, r=cuviper

Add benchmarks for `impl Debug for str`

In order to inform future perf improvements and prevent regressions, lets add some benchmarks that stress `impl Debug for str`.

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As I am currently working on improving the perf in rust-lang/rust#121150, its nice to have these benchmarks.

Writing them, I also saw that escapes are written out one char at a time, even though other parts of the code are already optimizing that via `as_str`, which I intend to do as well as a followup improvement.

r? ``@cuviper``
☝🏻 as you were also assigned to rust-lang/rust#121150, CC ``@the8472`` if you want to steal the review :-)

Author: matthiaskrgr