We need unambiguous, meaningful naming of stack reference operations dependent on how counting is done

https://github.com/faster-cpython/ideas/issues/700 describes three ways to count references:

• Virtual,
• Embedded, and
• Immediate

Virtual references are references that are know to exist to the relevant code generator, but are elided at runtime, so no API is needed for them.
Embedded references are marked by bit(s) in the reference and not in the ob_refcount field of the object.
Immediate references are counted in the ob_refcount (or free-threading equivalent) field of the object.

To this we should add uncounted which are references to immortal objects (including NULL).
Note that it is possible to have embedded or immediate references to immortal objects if the object was mortal when the reference, or reference this reference was created from, was created.

Why this matters

It is important that the use of references is understandable without referring to the implementation and we have multiple implementations of stackrefs, so the interface needs to be clear.

Multiple implementations

Even when we merge the free-threading and default implementations of stackrefs, we will still have the Py_STACKREF_DEBUG implementation which is very different and vital to finding reference errors.

Examples:

When creating an embedded stackref from another stackref, we should use PyStackRef_DUP_Embedded which has the same semantics as PyStackRef_DUP but creates an embedded reference if the implementation supports it.

There are circumstance when a method of counting is not safe. E.g. using embedded references in the heap is not safe. For that we will want to physically transform a reference without a logic change in ownership.
E.g. PyStackRef_ToNonEmbedded. In terms of ownership, this a no-op, PyStackRef_ToNonEmbedded(ref) is equivalent ref, but ensures that any embedded count is turned into an immediate count.

We probably should only use uncounted when referring to references in docs and comments, as we already have PyStackRef_FromPyObjectImmortal, there is no need for PyStackRef_FromPyObjectUncounted as well.

The issue names no files or tests, so first locate the stack-reference APIs and compare their existing implementations, including the debug implementation. Review the proposed Virtual, Embedded, Immediate, and uncounted terminology and the examples such as PyStackRef_DUP_Embedded and PyStackRef_ToNonEmbedded. Done means the operations have unambiguous names and their ownership and counting semantics are clear across implementations.