Issue 14612 - typeid(interface) returns TypeInfo_Class object

[9rnsr]

https://issues.dlang.org/show_bug.cgi?id=14612

Change the type of typeid(interface_obj) to TypeInfo_Interface, and fix TypeInfo object generation to support new TypeInfo hierarchy.

Requires corresponding druntime change: dlang/druntime#1295
Unfortunately, we need to fix compiler and druntime code at the same time.

[9rnsr]

Rebased on master, and ready for ddmd.

[yebblies]

I really think typeid(i) must be the same as typeid(cast(Object)i). Having it do anything other than get the concrete type will make it harder to use interfaces and abstract base classes interchangeably.

I understand that the current way makes sense with how interfaces are implement in D, but I think that implementation is supposed to be hidden from the user. I think it's obscure and unintuitive to the point where most experienced D users would not guess the behavior correctly.

When I use typeid(class or interface reference) I'm always trying to find out the dynamic type of the class. I don't ever care about the interface's adjusted vtable or other implementation details.

[dlang-bot]

Fix	Bugzilla	Description
✓	14612	typeid(interface) returns TypeInfo_Class object

[9rnsr]

I added more code to support incremental migration of dmd and druntime repositories.
Now this PR does not change anything. After the update of druntime, the new behavior will be introduced.