API Name: requestStorageAccessFor

[mreichhoff]

As the storage access API moves to {top-level site, embedded site} scoping, it begs the question of whether such a move is possible for rSAFor as well. That will likely be decided later, but naming can be made agnostic now.

The current name is also quite long.

requestStorageAccessFor still gets the point across, is shorter, and does not tie the API to a specific permission scope.

cc @johannhof