Switch to getting mono-api-[info|html] from a newly created repository we
control and where we can easily fix issues, since mono/mono isn't getting many
fixes anymore. In the past I know I've been reluctant to look at these tools,
just because of the hassle of setting things up to debug, and then the
paperwork to get the fixes in mono/mono, and then backported to the branch
where we need them.
This repo has a few other benefits:
* The tools are built using normal projects, which means they're easy to debug
in an IDE (mono/mono's code has generated project files, which used in-tree versions
of the BCL, and it got quite complex quite fast).
* One fewer dependency on the mono archive, so we're getting closed to be able
to drop it completely when we drop support for legacy Xamarin.
* #13669 is already fixed there.
* It contains a few other misc fixes.
Fixes https://github.com/xamarin/xamarin-macios/issues/13669.
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