Update language version to Dart 3 in examples (#178)

Author: parlough

examples/_animation/basic_hero_animation/pubspec.yaml

@@ -2,7 +2,7 @@ name: basic_hero_transition
 description: Shows how to create a simple or Hero animation using the Hero class directly.
 
 environment:
-  sdk: '>=2.18.5 <3.0.0'
+  sdk: ^3.0.0-0
 
 dependencies:
   flutter:

examples/_animation/basic_radial_hero_animation/pubspec.yaml

@@ -2,7 +2,7 @@ name: basic_radial_hero_transition
 description: Shows how to apply a radial transformation to the Hero as it animates to the new route.
 
 environment:
-  sdk: '>=2.18.5 <3.0.0'
+  sdk: ^3.0.0-0
 
 dependencies:
   flutter:

examples/_animation/basic_staggered_animation/pubspec.yaml

@@ -2,7 +2,7 @@ name: basic_staggered
 description: A new Flutter project.
 
 environment:
-  sdk: '>=2.18.5 <3.0.0'
+  sdk: ^3.0.0-0
 
 dependencies:
   flutter:

examples/_animation/hero_animation/pubspec.yaml

@@ -2,7 +2,7 @@ name: hero_animation
 description: Shows how to create a simple Hero transition.
 
 environment:
-  sdk: '>=2.18.5 <3.0.0'
+  sdk: ^3.0.0-0
 
 dependencies:
   flutter:

examples/_animation/radial_hero_animation/pubspec.yaml

@@ -2,7 +2,7 @@ name: radial_hero_animation
 description: Shows how to apply a radial transformation to the Hero as it animates to the new route.
 
 environment:
-  sdk: '>=2.18.5 <3.0.0'
+  sdk: ^3.0.0-0
 
 dependencies:
   flutter:

examples/_animation/radial_hero_animation_animate_rectclip/pubspec.yaml

@@ -2,7 +2,7 @@ name: radial_hero_animation_animate_rectclip
 description: Shows how to apply a radial transformation to the Hero as it animates to the new route.
 
 environment:
-  sdk: '>=2.18.5 <3.0.0'
+  sdk: ^3.0.0-0
 
 dependencies:
   flutter:

examples/_animation/staggered_pic_selection/pubspec.yaml

@@ -2,7 +2,7 @@ name: staggered_pic_selection
 description: A new Flutter project.
 
 environment:
-  sdk: '>=2.18.5 <3.0.0'
+  sdk: ^3.0.0-0
 
 dependencies:
   flutter:

examples/animation/animate0/pubspec.yaml

@@ -4,7 +4,7 @@ description: >
 version: 1.0.0
 
 environment:
-  sdk: '>=2.18.5 <3.0.0'
+  sdk: ^3.0.0-0
 
 dependencies:
   flutter:

examples/animation/animate1/pubspec.yaml

@@ -4,7 +4,7 @@ description: >
 version: 1.0.0
 
 environment:
-  sdk: '>=2.18.5 <3.0.0'
+  sdk: ^3.0.0-0
 
 dependencies:
   flutter:

examples/animation/animate2/pubspec.yaml

@@ -4,7 +4,7 @@ description: >
 version: 1.0.0
 
 environment:
-  sdk: '>=2.18.5 <3.0.0'
+  sdk: ^3.0.0-0
 
 dependencies:
   flutter: