Add namespace restrictions to Special:Block and API

Add namespace restrictions to Special:Block and API

This adds a UI for blocking namespaces to Special:Block
and a namespacerestrictions parameter to the block API.

The number of namespace restrictions in a single block
is not limited as page restrictions are.

The checkbox allowing the blocker to specify whether
the target can edit their own user page is normally
disabled for a partial block, but is re-enabled if
the block is to the user talk namespace.

If the config $wgBlockAllowsUTEdit is set to false, the
checkbox will not appear, and the target will not be
able to edit their own user talk page if they are
sitewide-blocked, namespace-blocked from the user talk
namespace, or page-blocked from their user talk page.

Bug: T204986
Change-Id: I9e231ad109d7285486ec332b26780339592b8df7