In recent zsh versions, `${(@ps:$sep:)var}` where $sep is a variable containing
a separator string and $var is a string with multiple values separated by $sep,
the `p` flag makes zsh correctly expand $sep before splitting $var. In versions
older than 5.0.8, this doesn't happen, so we use `eval` to get the same effect.

Fixes #10345

This reverts commit 63b7e576.

The GitHub UI might not remove CR characters from commit description forms
filled from a Windows browser.

This also allows the option to put extra paragraphs after the BREAKING CHANGE
message while properly displaying the breaking change message. Useful, for
example, to add signed-off or co-authored lines.

Fixes #9505

Also fixed a call to a defunct display:type-header function in displaying
breaking changes.