Add trim_prefix and trim_suffix methods for both slice and str types.

[deven]

Implements trim_prefix and trim_suffix methods for both slice and str types, which remove at most one occurrence of a prefix/suffix while always returning a string/slice (rather than Option), enabling easy method chaining.

Tracking issue

Closes #142312

API

impl str {
    pub fn trim_prefix<P: Pattern>(&self, prefix: P) -> &str;
    pub fn trim_suffix<P: Pattern>(&self, suffix: P) -> &str
    where
        for<'a> P::Searcher<'a>: ReverseSearcher<'a>;
}

impl<T> [T] {
    pub fn trim_prefix<P: SlicePattern<Item = T> + ?Sized>(&self, prefix: &P) -> &[T]
    where
        T: PartialEq;
    pub fn trim_suffix<P: SlicePattern<Item = T> + ?Sized>(&self, suffix: &P) -> &[T]
    where
        T: PartialEq;
}

Examples

// Method chaining
assert_eq!(" <https://example.com/> ".trim().trim_prefix('<').trim_suffix('>').trim(), "https://example.com/");

// Slices
let v = &[10, 40, 30];
assert_eq!(v.trim_prefix(&[10]), &[40, 30][..]);

ACP

Originally proposed in rust-lang/libs-team#597

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[deven]

r? @Amanieu