Auto merge of #137285 - yotamofek:pr/rustdoc/pulldown-escaping, r=GuillaumeGomez

librustdoc: Use `pulldown-cmark-escape` for HTML escaping

Implementation of `@notriddle` 's [suggestion](rust-lang/rust#137274 (comment)).
Somewhat related to #137274 , but the two PRs should be complementary.

Local perf results look like a nice improvement! (so would love a perf run on the CI)

Author: bors