Let's distinguish between the original pinned locals and the PinnedRegion locals.
The format need declarations if any are left over after transformations; the latter don't.
The C# translation of StObj will always apply delayed exceptions in these two cases, so putting an instruction with delayed exceptions in that slot would change program semantics.
The previously emitted `ref *(TTo*)(&source)` only compiles when `source` is a local variable; otherwise C# complains about the memory not being pinned.
Note that we special-case local variables to keep the previous behavior around; this avoids pulling in `System.Runtime.CompilerServices.Unsafe.dll` when it's unnecessary.
This initial commit only handles the trivial case where an Index or Range object is constructed.
The TODO portions of the test case show there are plenty of cases where where the C# compiler emits more complex code patterns that will require ILAst transforms.
If this attribute is in use, private/internal members lack nullability annotations.
Previously in such cases, we ended up inheriting the nullability from the `[NullableContext]`, which could cause us to display a misleading nullability for primary methods.
In debug builds, it could also trigger an assertion when trying to apply the "nullable reference type" marking to to value types.
Of note is that properties and events are a special case: they do not explicitly store Accessibility in metadata. For properties computing the accessibility requires decoding the signature (to find overridden base properties). So these two only check the declaring type's accessibility instead; private properties may still carry nullability despite `[NullablePublicOnly]`. However, the property accessors won't store nullability, so we need to read the `returnTypeAttributes` from the property itself.