Ensure option names updated to match path

[cmacmackin]

Previously, using the move-assignment operator for Options objects would keep the same full name as the moved object. This was problematic because it meant that the name of the newly-assigned Options object could differ from the path used to access that object. E.g.,

Options opts;
// Add various things in options
opts["a"]["b"] = opts["c"]["d"].copy();
fmt::print("{}\n", opts["a"]["b"].str()); // Output: c:d

This posed particular problems for the permissions system in Hermes-3, as it meant that the name being checked against permissions could be incorrect.

In this PR I've modified the move-assignment operator to ensure that the assigned-to Options object (and all children) will have names consistent with the path to access them.

[github-actions]

clang-tidy made some suggestions

[cmacmackin]

Thanks for the speedy turnaround on this, but unfortunately I just realised there is a corner-case I missed. I'll open another PR for that.