[sgen] Implement api for allocating pinned arrays (#34398)

[sgen] Implement api for allocating pinned arrays (#34398)

* [sgen] Add support for allocating pinned array

These objects will end up allocated either in LOS (which is by design not moved around) or into special major blocks where compaction doesn't take place.

* [sgen] Be consistent with coreclr on GC api

* Enable GC tests for pinned array allocation

* Skip large array allocation test on mono