Updates to generics design details, part 2

[josh11b]

Continued from part 1: #3231. Second step updating docs/design/generics/details.md. There remains some work to incorporate proposal #2200.

• The biggest changes are incorporating much of the text of proposals:
  • Associated constant assignment versus equality #2173
  • Termination algorithm for impl selection #2687
• It incorporates changes from proposals:
  • Member access expressions #989
  • Rework operator interfaces #1178
  • Checked and template generic terminology #2138
  • Template generics #2200
  • Types are values of type type #2360
  • Expression phase terminology #2964
  • Reduce ambiguity in terminology #3162
• It also updates the text to reflect the latest thinking from leads issues:
  • Generic let with auto? #996
  • Checked generics calling templates #2153 -- most notably deleting the section on TypeId.
• Update to rule for prioritization blocks with mixed type structures from discussion on 2023-07-18
• Adds reference links to proposals, issues, and discussions relevant to the text.
• Also tries to use more precise language when talking about implementations, to avoid confusing impl declaration and definitions with the impls operator used in where clauses, an issue brought up in
  • Keyword to use in place of is in where...is constraints #2495
  • Replace keyword is with impls #2483

[zygoloid]

(Checkpoint of incomplete review)

[zygoloid]

Thanks, I think we're basically converged here. I'm happy to take another look if you like after the Container example is fixed, but I don't feel it's necessary.

[zygoloid]

This is doing name lookup on the next line: where .ElementType = is looking up ElementType in the incomplete interface Container (after the declaration of ElementType), and .SliceType = is looking up the member that we're in the middle of declaring. I think this example needs to be reworked a bit.