Rollup merge of #134316 - zachs18:string_replace_in_place_rebase, r=joshtriplett

Add `String::replace_first` and `String::replace_last`

Rebase of #97977 (cc `@WilliamVenner)`

> Convenience methods that use `match_indices` and `replace_range` to efficiently replace a substring in a string without reallocating, if capacity (and the implementation of `Vec::splice`) allows.

The intra-doc link to `str::replacen` is a direct url-based link to `str::replacen` in `std`'s docs to work around #98941. This means that when building only `alloc`'s docs (and not `std`'s), it will be a broken link. There is precedent for this e.g. in [`core::hint::spin_loop`](https://doc.rust-lang.org/nightly/src/core/hint.rs.html#214) which links to `std::thread::yield_now` using a [url-based link](https://github.com/rust-lang/rust/blob/master/library/core/src/hint.rs#L265) and thus is a dead link when only building `core`'s docs.

ACP: rust-lang/libs-team#506

Author: jhpratt