Generalize and inline slice::fill specializations

[the8472]

This makes the memset specialization applicable to more types. And since the code now lives in a generic method it is also eligible for cross-crate inlining which should fix #83235

[rust-highfive]

r? @joshtriplett

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[the8472]

Odd, this didn't show up when running tidy locally.

[Xanewok]

@bors try @rust-timer queue

[rust-timer]

Awaiting bors try build completion.

@rustbot label: +S-waiting-on-perf

[bors]

⌛ Trying commit d7fdd90 with merge ce671292e8a00a0c94483a1fe89485bb08d4762b...

[bors]

☀️ Try build successful - checks-actions
Build commit: ce671292e8a00a0c94483a1fe89485bb08d4762b (ce671292e8a00a0c94483a1fe89485bb08d4762b)

[rust-timer]

Queued ce671292e8a00a0c94483a1fe89485bb08d4762b with parent 36f1f04, future comparison URL.

[rust-timer]

Finished benchmarking try commit (ce671292e8a00a0c94483a1fe89485bb08d4762b): comparison url.

Benchmarking this pull request likely means that it is perf-sensitive, so we're automatically marking it as not fit for rolling up. Please note that if the perf results are neutral, you should likely undo the rollup=never given below by specifying rollup- to bors.

Importantly, though, if the results of this run are non-neutral do not roll this PR up -- it will mask other regressions or improvements in the roll up.

@bors rollup=never
@rustbot label: +S-waiting-on-review -S-waiting-on-perf

[the8472]

@rustbot label T-libs-impl

[m-ou-se]

Thanks!

@bors r+

[bors]

📌 Commit d7fdd90 has been approved by m-ou-se

[bors]

⌛ Testing commit d7fdd90 with merge 1010038...

[bors]

☀️ Test successful - checks-actions
Approved by: m-ou-se
Pushing 1010038 to master...