Change interners to start preallocated with an increased capacity
Inspired by https://github.com/rust-lang/rust/issues/137005.
Added a `with_capacity` function to `InternedSet`. Changed the `CtxtInterners` to start with `InternedSets` preallocated with a capacity.
This *does* increase memory usage at very slightly(by ~1 MB at the start), altough that increase quickly disaperars for larger crates(since they require such capacity anyway).
A local perf run indicates this improves compiletimes for small crates(like `ripgrep`), without a negative effect on larger ones.