If links get pasted into VE and they lack a "//" in the `href`, they
are automatically considered to be "internal", thus being converted into
`[[...]]` wikitext links.
In case of pseudo protocols like `mailto:` this should not be the case.
This patch uses MediaWiki core settings to check if a `href` value is an
external protocol known to the application.
Bug: T297575
Depends-On: I2e584f6d5adc6b2d735e79cea64f2beeb5f2c36d
Change-Id: I2b383106450e02cc6bcc1b99d547ff2ed7832b4c
Previous attempt in 005a8d24ef,
reverted in 3c1d167b33.
The deduplicateStyles() function lacked a check for fosterable
positions, which caused T299767. This is now fixed.
Also added tests.
Bug: T287675
Bug: T299251
Change-Id: I0d22be9b66d26d09373cee63dd6ce52c1659e62d