fix: migrate MaterialStateProperty usage

[drown0315]

Migrated all usages of MaterialStateProperty.all, This is because MaterialStateProperty.all will be deprecated in the future. just only change example and websites, so does not update CHANGELOG.md refer to: https://github.com/dart-lang/sdk/issues/49056.

e.g. Replace MaterialStateProperty.all to MaterialStatePropertyAll Before:

            ElevatedButton(
              style: ButtonStyle(
                // If there is an error, we show the button in red
                backgroundColor: MaterialStateProperty.all(
                  isErrored ? Colors.red : null,
                ),
              ),

After:

            ElevatedButton(
              style: ButtonStyle(
                // If there is an error, we show the button in red
                backgroundColor: MaterialStatePropertyAll(
                  isErrored ? Colors.red : null,
                ),
              ),

Checklist

Before you create this PR confirm that it meets all requirements listed below by checking the relevant checkboxes ([x]).

• [ ] I have updated the CHANGELOG.md of the relevant packages. Changelog files must be edited under the form:

  ## Unreleased fix/major/minor
  
  - Description of your change. (thanks to @yourGithubId)

• [x] If this contains new features or behavior changes, I have updated the documentation to match those changes.

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Latest commit: 5752b499b8beef1e419ade681785908272fe4a4f

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[rrousselGit]

Hello!

There are a few conflicts :) I personally migrated to WidgetsStateProperty instead

[drown0315]

Just noticed that you have already completed the migration.

I have resolved these conflicts.

I found that WidgetStateProperty has not been released in the latest stable version of Flutter yet, which may cause errors for many developers running examples, so I think temporarily using MaterialStatePropertyAll might be a better option.

[rrousselGit]

I've already migrated the english variant to use WidgetsStateProperty.

I prefer being on the edge in terms of feature, because otherwise we'll have to updates the docs again later.

[drown0315]

Okay, I have updated. I replace all occurrences of MaterialStateProperty.all with WidgetStatePropertyAll

[gdurandrexel]

You might want to use ElevatedButton.styleFrom instead of ButtonStyle, to avoid bothering with these XxxPropertyAll.

[rrousselGit]

LGTM