Tighten the URL warnings

[dd32]

On translate.wordpress.org we have two types of URL warnings

• GlotPress mismatching tag warning which detect mis-matched <a href="..."> tags

and

• A custom warning to detect URL changes outside of tags in the content

The latter allows for certain URL changes (ie. wordpress.org to fr.wordpress.org, and http to https) however the former doesn't.
We should extend the GlotPress warning to ignore any valid URL changes.

It also looks like we should probably ignore urls which only differ by a trailing slash being added, which while a change that may break a URL is highly unlikely to.

[dd32]

In 10688:

Translate: Extend the GlotPress HTML warnings to allow certain URL domain changes.

This alows for <a href="http://wordpress.org/.."> to be translated to <a href="https://test.wordpress.org/.."> without generating a warning.

See #5155.

[dd32]

In 10689:

Translate: Allow for the trailing slash to be altered on plaintext urls.

This avoids triggering an error when http://wordpress.org is translated to https://wordpress.org/.

This will still trigger a warning on a trailing slash changing inside a HTML tag like <a href="..">.

See #5155.

[dd32]

Would be great to better ​handle warnings like these:

The translation appears to be missing the following URLs: https://example.com</li><li>-
The translation contains the following unexpected URLs: https://example.com</li><li

URLs can include < but realistically it's not going to happen in translations.

[dd32]

In 10730:

Translate: Expand upon the GlotPress tag warnings to validate the href values separately to the rest of the tags.

This change also allows for the tags to be translated in any order, but doesn't validate the HTML is correctly nested (follow up change needed)

See #5155.

[dd32]

In 10733:

Translate: When matching URLs in text, assume a URL will not contain a HTML tag, so exclude < from appearing within the URL.

Fixes #5155.