editor: vector n-slicer should clamp all shapes contained

Previously, i thought it'd be nice to let vertices outside the bounds of the NSlicer to move relative to the bounds. You could get to this state by manually changing the intrinsic size to be smaller, so some vertices that used to be within bounds are now considered out.

However, I think this could be kinda confusing, not to mention harder to implement correctly (e.g. if the node is flipped, then the vertices outside the bounds also need to be flipped). I think not a lot of people will manually go and change the intrinsic size, so the simpler thing to do is to just clip everything:
<img width="1030" alt="image" src="https://github.com/user-attachments/assets/fc19caed-edce-4c15-bc3b-6d0e5f9496fc">

Diffs=
afcf0992da editor: vector n-slicer should clamp all shapes contained (#8428)

Co-authored-by: Susan Wang <susan@rive.app>

.rive_head

@@ -1 +1 @@
-c7de07c0ca5e766fd2050ea87ac0b48e9714df63
+afcf0992da4e4982243b7fa1c51c93b76a5bcb64

src/math/n_slicer_helpers.cpp

@@ -102,11 +102,6 @@ float NSlicerHelpers::mapValue(const std::vector<float>& stops,
                                const ScaleInfo& scaleInfo,
                                float value)
 {
-    if (value < (stops.front() - 0.001) || value > (stops.back() + 0.001))
-    {
-        return value;
-    }
-
     float result = 0;
     for (int i = 0; i < (int)stops.size() - 1; i++)
     {