Codexify strips spaces in titles

[ocean90]

Report: ​https://wordpress.org/support/topic/forum-bugs-and-broken-things/#post-8240018

It appears the forum’s double bracket Codex link shortcut is stripping spaces instead of replacing with underscores. When I do [[Hardening WordPress]] the link becomes codex.wordpress.org/HardeningWordPress which is missing the underscore that used to be inserted for the space.

Input: [[Hardening WordPress]]
Actual output: <a href="https://codex.wordpress.org/HardeningWordPress" rel="nofollow">HardeningWordPress</a>
Expected output: <a href="https://codex.wordpress.org/Hardening_WordPress" rel="nofollow">Hardening WordPress</a>

Plugin: https://meta.trac.wordpress.org/browser/sites/trunk/wordpress.org/public_html/wp-content/plugins/wporg-bbp-codexify

[jmdodd]

In 4175:

Support Forums: Replace spaces with underscores in Codex link shortcut.

Codex link shortcuts were incorrectly stripping spaces from the link and title rather than replacing them with an underscore.

Props SergeyBiryukov.
Fixes #2103.