Auto merge of #52994 - varkor:trim_direction, r=alexcrichton
Add trim_start, trim_end etc.; deprecate trim_left, trim_right, etc. in future
Adds the methods: `trim_start`, `trim_end`, `trim_start_matches` and `trim_end_matches`.
Deprecates `trim_left`, `trim_right`, `trim_left_matches` and `trim_right_matches` starting from Rust 1.33.0, three versions from when they'll initially be marked as being deprecated, using the future deprecation from https://github.com/rust-lang/rust/issues/30785 and https://github.com/rust-lang/rust/pull/51681.
Fixes https://github.com/rust-lang/rust/issues/30459.