[registrar] Support 'out' parameters from NULL pointers. Fixes#54919.
Native code doesn't have the 'out' and 'ref' distinction C# has, and passes
NULL around left and right.
So make sure the generated code from the static registrar doesn't write to such NULLs.
https://bugzilla.xamarin.com/show_bug.cgi?id=54919
Generate trampoline and registrar tests that tests if a return type requires objc_msgSend or objc_msgSend_stret.
Now it's much easier to test new return types (a single line of code), which
avoids a _lot_ of copy-pasting, and makes sure all the different variations
are tested properly.
These new tests found several bugs, which are fixed in subsequent commits.
* [tests] Remove Classic SDK tests.
* Remove XI/Classic support.
This also means we can remove support for the legacy registrars.
* [monotouch-test] Remove legacy registrar tests.
* [tests/mtouch] Remove Classic tests (and legacy registrar logic).
* [tests/scripted] Fix tests to reference Xamarin.iOS.dll.
Support binding NSObjects as IntPtr. This is usually not
a problem, because when we fetch the ObjC signature for a
method, we usually get the signature as exported by us,
(in which case a parameter bound as 'IntPtr' would be treated
as 'void *' in the dynamic registrar) *except* when the
selector corresponds with a protocol the type implements,
in which case we get the signature as defined in the protocol.
https://bugzilla.xamarin.com/show_bug.cgi?id=41132
Rolf Bjarne Kvinge