Add 'select all points' method to ShapeState struct

[gautamprikshit1]

Closes #1318

[Keavon]

!build

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[Keavon]

This looks pretty good from my QA testing. However upon playing with it, realized it would probably be more useful to people if it selects all the anchors but not the handles. And if existing handles are already selected, I think(?) we want to just overwrite that by deselecting all the handles and selecting all the anchors. Would you mind making those changes, please?

[Keavon]

!build

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[Keavon]

There is one other bug I'm noticing which you didn't cause, but it's a bug that interacts with the feature you're adding. I was wondering if you could take on the extra challenge to try and fix it too. Currently, if you have multiple points selected, clicking on one of those selected points (which deselects all but then re-selects that one clicked point) doesn't update the overlays so it visually appears like that click didn't do anything (however, if you hit G to move the selected points around, you'll see how it's indeed the one point that's selected).

So the fix is to find where to update the overlays for this specific code path.

[Keavon]

!build

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[Keavon]

Awesome 🎉