Invoke temporary materialization conversion directly rather than
handwaving about a temporary object. Specify that the o expression is
evaluated. Bulletize description of the three different ways that
await-suspend is called.

Fix wording that uses values and objects on the left-hand side of a
class member access to instead consistently use expressions.

Fixes #2774.

conventions.

Reorder and rearrange to reduce the number of variables with long scopes
that we define in the wording.

Fix mismatch between core and library wording where library permits
coroutine_handle<void> to resume a coroutine with any promise type, and
the core language does not.