first stab at having lottie assets behave as a folder

mostly want to show the interaction @alxgibsn

I still need to add tests, I also want to deal with uploading assets multiple times...

https://user-images.githubusercontent.com/1216025/204879568-ac9c53c9-1ced-486b-a78a-d7918ba30be1.mov

(as you can see in the video, assets get added individually as subassets, which get uploaded and takes a while, this is something i'm going to address first, so that we don't get stuck re uploading assets, there's also some drag and drop that was included with assets, you can reorder assets inside the lottie asset with this.. i'm not sure if its really worth having, or if i should see if we can disable it)

Diffs=
49df25d5a first stab at having lottie assets behave as a folder (#4483)
2a53e702a Get Rive tests compiling and running on MSVC
1733f0c5a Add Mat2D::mapPoints, optimized in SIMD
18aaa8cb5 explicitly include <iterator> for linux builds (#4467)
a954c197a Core text editing (#4446)
df91086ce Only __builtin_reduce_add for integer types
4e221ab4f Add Mat2D::findMaxScale()
362c448b3 Add more features to simd.hpp
210e0ab14 Add gradient animation steps (#4451)
5d661f39a Text in core (#4439)

.rive_head

@@ -1 +1 @@
-12c6ee13010f1f73354358ae169e4f81e646b8be
+49df25d5a4056efcdfe8c3220ea51a113475f420

analysis_options.yaml

@@ -4,6 +4,9 @@ analyzer:
     implicit-dynamic: false
   errors:
     unused_import: error
+  exclude:
+    - ios
+    - macos
 
 linter:
   rules: