Optimized string search / trim / slice methods

https://github.com/oxc-project/oxc/pull/6151 introduced string search routines optimized for ASCII strings for parsing JSX pragmas.

These routines could be generalized and put in their own crate.

We use functions like str::trim all over the codebase, but it's quite slow as it handles non-ASCII characters in its hot path. But typical JS code which Oxc processes is almost entirely ASCII, so we can benefit from routines optimized for ASCII, which handle non-ASCII characters in a cold path.

trim_end introduced in https://github.com/oxc-project/oxc/pull/6151 is a great deal smaller and faster on its hot ASCII path than std::str::trim_end: https://godbolt.org/z/4nfW6183z

We can also provide optimized string search routines where the character being searched for is ASCII (typical usage).

We may want to replicate Rust's nightly std::ascii::Char or reuse parts of the ascii crate.

Review PR #6151 and the string search routines it introduced first. Determine the crate and API scope for ASCII-optimized trim, search, and slice methods, including non-ASCII handling, then compare the routines with the standard library using the linked Godbolt example or equivalent benchmarks.