[basic.scope.pdecl], [temp] Replace "expansion statement" with "expansion-statement"

[eisenwave]

Fixes NB US 2-404 (C++26 CD).
Also fixes https://github.com/cplusplus/nbballot/issues/585.

This PR does a little bit more than the NB comment asked for. We have the bad language of

for-range-declaration of an expansion statement

and

compound-statement of an expansion statement

The NB comment only relates to the second case, but in general, if we talk about one grammatical thing being inside another, we should consistently use grammar font.

[jensmaurer]

Those are all statements about grammar, so referring to the grammarterm expansion-statement is correct.