[Feature Request] Reflection: inspect a type's attributes via `attributesof` or similar

[NotsoanoNimus]

At the moment, C3 does not have a way to inspect the attributes associated with a user-defined type. This would be a nice feature beyond the existing tagging feature because conditional behavior for the presence of builtin attributes could apply as well.

Here's a very contrived example:

// Sample changes to Standard Library code
<*
 @require $Type.alignof <= mem::DEFAULT_MEM_ALIGNMENT : "Types with alignment exceeding the default must use 'alloc_aligned' instead"
*>
macro alloc(Allocator allocator, $Type) @nodiscard
{
	$if @in("mustinit", ...$Type.attributesof):
		return ($Type*)calloc(allocator, $Type.sizeof);
	$else
		return ($Type*)malloc(allocator, $Type.sizeof);
	$endif
}
// ========================
struct MyType @mustinit   // assume `mustinit` is a built-in C3 language attribute
{
    int a;
    int b;
} 
MyType* x = alloc::alloc(mem, MyType);   // here, the buffer is now implicitly zeroized

Clarification: It's possible to define MyType here with a custom attribute that includes a tag - e.g., attrdef @ForceInit = @mustinit, @tag("force_init", 1); - but the key point of this request is to be able to inspect those C3 builtin attributes without the tags and attrdef at all.