[3.x] VisibilityEnabler2D - rename hide_parent and change default

[lawnjelly]

Renames "parent_visibility" to "hide_parent", and changes the default to off to preserve backward compatibility.

Notes

• My fault here, I approved [3.x] Add option in VisibilityEnabler2D to hide the parent for better performance (reverted) #63193 before these suggested changes were made.
• These are the previously agreed upon changes, I'll also do a follow up PR to make the flags more sensible, as they will require more careful review.

[lawnjelly]

Actually hold off on this, I've been doing the flags PR and it is actually a barrel of worms, so I'm re-evaluating whether it would be better to revert #63193 and just rely on #68738 instead (which does all this server side, so doesn't suffer from the flag logic problems).

[akien-mga]

Superseded by #78182.