rustdoc: Add CrateName newtype (#13056)

This PR adds a `CrateName` newtype used to represent crate names.

This makes the code a bit more self-descriptive and prevents confusing
other string values for a crate name.

It also changes the internal representation from a `String` to an
`Arc<str>` for cheaper clones.

Release Notes:

- N/A

Cargo.lock

@@ -8714,6 +8714,7 @@ dependencies = [
  "anyhow",
  "async-trait",
  "collections",
+ "derive_more",
  "fs",
  "futures 0.3.28",
  "fuzzy",