feat: add runtime layout fit type for ios, android, web

First steps towards supporting artboard resizing in our runtimes. This PR includes:
- New Fit type `autoResizeArtboard`. After a bit of back and forth, I think this keeps the API simple.
- ScaleFactor which represents a scale value to scale the artboard by in addition to resizing (only applies with `autoResizeArtboard`). This may be useful because an artboard is created at a specific width/height, but it may be deployed to platforms where it is rendered to a much smaller or larger surface/texture. Currently the default is 1.0 (no scale), however, an alternative is to have it default to something like textureSize / artboardSize so we sort of auto normalize it.
- Implemented on iOS. Once this is finalzed, we can work with DevRels to implement across all runtimes.
- TODO : Bubble up an event when the artboard size is changed internally by the .riv

https://github.com/user-attachments/assets/20e9fdda-5c3e-4f3f-b2f5-104ff0291fbe

Diffs=
e71b4cc081 feat: add runtime layout fit type for ios, android, web (#8341)

Co-authored-by: CI <pggordonhayes@gmail.com>
Co-authored-by: David Skuza <david@rive.app>
Co-authored-by: Philip Chung <philterdesign@gmail.com>

.rive_head

@@ -1 +1 @@
-c64659be84f36d2855173491d6bcab8255c50950
+e71b4cc081aad43f304589d7233fe2d8065fda85

include/rive/layout.hpp

@@ -10,7 +10,8 @@ enum class Fit : unsigned char
     fitWidth,
     fitHeight,
     none,
-    scaleDown
+    scaleDown,
+    layout
 };
 
 class Alignment

include/rive/renderer.hpp

@@ -26,7 +26,11 @@ class Vec2D;
 
 // Helper that computes a matrix to "align" content (source) to fit inside frame
 // (destination).
-Mat2D computeAlignment(Fit, Alignment, const AABB& frame, const AABB& content);
+Mat2D computeAlignment(Fit,
+                       Alignment,
+                       const AABB& frame,
+                       const AABB& content,
+                       const float scaleFactor = 1.0f);
 
 enum class RenderBufferType
 {
@@ -183,9 +187,11 @@ public:
     void align(Fit fit,
                Alignment alignment,
                const AABB& frame,
-               const AABB& content)
+               const AABB& content,
+               const float scaleFactor = 1.0f)
     {
-        transform(computeAlignment(fit, alignment, frame, content));
+        transform(
+            computeAlignment(fit, alignment, frame, content, scaleFactor));
     }
 };
 } // namespace rive

src/renderer.cpp

@@ -7,7 +7,8 @@ using namespace rive;
 Mat2D rive::computeAlignment(Fit fit,
                              Alignment alignment,
                              const AABB& frame,
-                             const AABB& content)
+                             const AABB& content,
+                             const float scaleFactor)
 {
     float contentWidth = content.width();
     float contentHeight = content.height();
@@ -52,6 +53,10 @@ Mat2D rive::computeAlignment(Fit fit,
             scaleX = scaleY = minScale;
             break;
         }
+        case Fit::layout:
+        {
+            return Mat2D::fromScale(scaleFactor, scaleFactor);
+        }
         case Fit::none:
         {
             scaleX = scaleY = 1.0f;