This PR introduces `AnimationStyle`, it is used to override default
animation curves and durations in several widgets.

fixes [Add the ability to customize MaterialApp theme animation
duration](https://github.com/flutter/flutter/issues/78372)
fixes [Allow customization of showMenu transition animation curves and
duration](https://github.com/flutter/flutter/issues/135638)
fixes [`AnimationStyle.noAnimation` needs to replace `AnimatedTheme`
with just `Theme` in the
`MaterialApp`](https://github.com/flutter/flutter/issues/138618)

Here is an example where popup menu curve and transition duration is
overridden:

```dart
          popUpAnimationStyle: AnimationStyle(
            curve: Easing.emphasizedAccelerate,
            duration: Durations.medium4,
          ),
```

Set `AnimationStyle.noAnimation` to disable animation.
```dart
    return MaterialApp(
      themeAnimationStyle: AnimationStyle.noAnimation,
```

## Pre-launch Checklist

- [x] I read the [Contributor Guide] and followed the process outlined
there for submitting PRs.
- [x] I read the [Tree Hygiene] wiki page, which explains my
responsibilities.
- [x] I read and followed the [Flutter Style Guide], including [Features
we expect every widget to implement].
- [x] I signed the [CLA].
- [x] I listed at least one issue that this PR fixes in the description
above.
- [x] I updated/added relevant documentation (doc comments with `///`).
- [x] I added new tests to check the change I am making, or this PR is
[test-exempt].
- [x] All existing and new tests are passing.

If you need help, consider asking for advice on the #hackers-new channel
on [Discord].

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[test-exempt]:
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[Flutter Style Guide]:
https://github.com/flutter/flutter/wiki/Style-guide-for-Flutter-repo
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