[runtime] Add mono_class_load_from_name and mono_class_try_load_from_name.

[runtime] Add mono_class_load_from_name and mono_class_try_load_from_name.

Those are variants of mono_class_from_name_checked that implement two common type loading scenarios in the rutime.

The first is mono_class_load_from_name, that loads critical types that the runtime cannot function without.
This means we abort if the type is missing or broken. We should use it in places where today we crash when
either of those would happen.

The other is mono_class_try_load_from_name, which is ok if the type is not found, but will abort if the type is broken.
The reasoning for aborting on a broken type is that it's unclear on whether the runtime should be using the type or not,
specially given most of those optional types change behavior of the application. This, in practice, forces the linker to
not produce a broken corlib.