Replace some std::iter::repeat with str::repeat

[ghost]

I noticed that there were some instances where std::iter::repeat would be used to repeat a string or a char to take a specific count of it and then collect it into a String when str::repeat is actually much faster and better for that.

See also: rust-lang/rust-clippy#7260.

[rust-highfive]

Some changes occurred in src/tools/clippy.

cc @rust-lang/clippy

[rust-highfive]

r? @Mark-Simulacrum

(rust-highfive has picked a reviewer for you, use r? to override)

[Mark-Simulacrum]

@bors r+ rollup=never

[bors]

📌 Commit edd38a936d1dec1d3fe5c4857185ccd21c44d1b3 has been approved by Mark-Simulacrum

[Mark-Simulacrum]

@bors r-

[Mark-Simulacrum]

Please squash out the merge(?) commit.

[ghost]

Done. I just realized that the changes I made in src/tools/clippy/clippy_lints/* were useless because it's not the upstream code, sooner or later the actual code will be pulled from https://github.com/rust-lang/rust-clippy. In rust-lang/rust-clippy#7265 these changes I made here are included but for the future shouldn't changes to src/tools/clippy/clippy_lints/* in this repository be disallowed or shouldn't @rust-highfive give some kind of warning? It could potentially avoid confusion and good changes being lost.

[Mark-Simulacrum]

That directory is synced both ways, changes to it are fine to make here.

[bors]

☔ The latest upstream changes (presumably #85954) made this pull request unmergeable. Please resolve the merge conflicts.

[Mark-Simulacrum]

@bors r+ rollup=never

[bors]

📌 Commit c08ea17 has been approved by Mark-Simulacrum

[bors]

⌛ Testing commit c08ea17 with merge e82b650...

[bors]

☀️ Test successful - checks-actions
Approved by: Mark-Simulacrum
Pushing e82b650 to master...