Editorial: make single-implementation concrete methods into abstract operations

[bakkot]

AOs are generally nicer for readers (and tooling).

I've left these where they were and just changed their type, but since each section is preceded by a sentence like

The behaviour of the additional concrete specification methods for Function Environment Records is defined by the following algorithms:

we should probably also either reword that sentence or move these somewhere else.

Commits can be reviewed individually but should land as a single commit.

[jmdyck]

(Reading the commit titles, I wondered, "Why not HasRestrictedGlobalProperty?" But I see it's handled in the commit for CanDeclareGlobalVar.)