Tidyup varfont_shader_puzzle (#1629)

* Tidyup `varfont_shader_puzzle`

* Add a rebuild script and a test

* Simplify fragment shaders

* Drop web

* Enable `beta` CI

* make it `beta` inclusive

* Pull out the program loading code

experimental/varfont_shader_puzzle/codelab_rebuild.yaml

@@ -0,0 +1,19 @@
+# Run with tooling from https://github.com/flutter/codelabs/tree/main/tooling/codelab_rebuild
+name: Animations rebuild script
+steps:
+  - name: Remove runners
+    rmdirs: 
+      - android
+      - ios
+      - linux
+      - macos
+      - windows
+  - name: Flutter recreate
+    flutter: create . --platforms android,ios,linux,macos,windows
+  - name: Strip DEVELOPMENT_TEAM
+    strip-lines-containing: DEVELOPMENT_TEAM =
+    path: ios/Runner.xcodeproj/project.pbxproj
+  - name: Build for iOS
+    flutter: build ios
+  - name: Build for macOS
+    flutter: build macos