[flang] Lowering and implementation for extends_type_of

[flang] Lowering and implementation for extends_type_of

Add implementation and loweirng for the extends_type_of
intrinsic.

The standard mentions this: otherwise if the dynamic type of A or MOLD is
extensible, the result is true if and only if the dynamic type of A is an
extension type of the dynamic type of MOLD. Which could be interpreted that
`extends_type_of(a, a)` could be false since a type is not an extension of
itself. Gfortran result for this is `true` so the same behavior is applied
here as well.

Depends on D141364

Reviewed By: jeanPerier, PeteSteinfeld

Differential Revision: https://reviews.llvm.org/D141376