[stmt.do] Add grammar equivalence and reorder paragraphs

[Eisenwave]

Fixes #6492 for the most part.

This edit improves a few things:

1. The two paragraphs are swapped, which creates symmetry with how they are ordered in [stmt.while]
2. Similar to while and for, the equivalence to a goto construct is also provided.
   Note that the trailing semicolon issue is swept under the rug by defining the equivalence for while (expression); with a semicolon present
3. \grammarterm is used in a few more places.

[jensmaurer]

This shouldn't go in without CWG seeing it.