gh-98154: Clarify Usage of "Reference Count" In the Docs (gh-107552)

gh-98154: Clarify Usage of "Reference Count" In the Docs (gh-107552)

PEP 683 (immortal objects) revealed some ways in which the Python documentation has been unnecessarily coupled to the implementation details of reference counts.  In the end users should focus on reference ownership, including taking references and releasing them, rather than on how many reference counts an object has.

This change updates the documentation to reflect that perspective.  It also updates the docs relative to immortal objects in a handful of places.