* PEP 696: consolidate discussion of constraint solving.
Consolidates discussion of usage of defaults in constraint solving in
the "Function Defaults" section, to make it clear that this is
experimental and unspecified.
* PEP 696: Explicitly call out that defaults do not affect subtyping.
* Moves TypeVarTuple discussion so the text flows better. Otherwise, it
feels to me like an awkward interlude between the paragraph
introducing rules and the actual rules.
* In sections where the text uses `T1` and `T2` as TypeVar names, changes
the examples to use the same names.
* Fix subtyping relationship in "Bound Rules."
* Spell out subclassing rules in the text, rather than leaning so much on the example.
Co-authored-by: Jelle Zijlstra <jelle.zijlstra@gmail.com>
Co-authored-by: James Hilton-Balfe <gobot1234yt@gmail.com>