ve.ui.MWExtensionInspector: Prevent from setting impossible content

XML-like tags in wikitext are not actually XML and don't expect
their contents to be escaped. This means that (usually) it is not
possible for a tag '<foo>…</foo>' to contain the string '</foo>'
(see bug 57429 comment 4 for details).

Prevent the user from doing that by escaping the first angle bracket
'<' to '&lt;' in such inputs when the inspector closes.

Bug: 57429
Change-Id: Ia566452ae0ffc9caa3ea48a52e5b8032c33fc9c8
ve.ce.MWExtensionNode: Don't escape content of wikitext tags on preview

XML-like tags in wikitext are not actually XML and don't expect their
contents to be escaped. The contents are usually not parsed as
HTML/XML anyway.

It means that it is not possible for a tag '<foo>…</foo>' to contain
the string '</foo>', but that is prevented by change Ia566452a.

Bug: 57429
Change-Id: I2516a897c85b4a3b79a34ff6cad5d124fbc30170
Merge "ve.ui.MWExtensionInspector: Prevent from setting impossible content"
Merge "ve.ce.MWExtensionNode: Don't escape content of wikitext tags on preview"