Minor 1.36 rustdoc regression: \] after a link is not treated as an escape

[MaulingMonkey]

A minor change in behavior between 1.35.0 and 1.36.0. Repro example here:

/// \[This escapes both brackets\]
/// \[[This escapes only the left bracket as of 1.36.0](https://www.google.com/)\]
pub fn example() {
}

Run a standard cargo doc. In 1.36.0, the link will display \] instead of ] after the link, whereas in 1.35 it will display ] after the link.

[ehuss]

I filed pulldown-cmark/pulldown-cmark#375 for this.