Update Dart dependency version and changelog

[helin24]

This updates Dart dependency to last public release and cleans up the changelog in anticipation of the next release.

Make sure the plugin builds and changelog appears as expected in the plugin page.

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Review the contribution guidelines below:

• I’ve reviewed the contributor guide and applied the relevant portions to this PR.
• I've included the required information in the description above.
• My up-to-date information is in the AUTHORS file.
• I've updated CHANGELOG.md if appropriate.

Contribution guidelines:

• See
  our contributor guide and
  the Flutter organization contributor guide
  for general expectations for PRs.
• Larger or significant changes should be discussed in an issue before creating a PR.
• Dart contributions to our repos should follow the Dart style guide and use
  dart format.
• Java and Kotlin contributions should strive to follow Java and Kotlin best
  practices (discussion).

[gemini-code-assist]

Code Review

This pull request prepares for the release of version 96.0.0 by updating the changelog and bumping the dartPluginVersion to 508.1.0 in gradle.properties. Feedback was provided on a changelog entry that violates the repository style guide by starting with the verb "Fixed" instead of using a descriptive, state-based phrase.