fix(package_info_plus): Make example app content scrollable

[vbuberen]

Description

While testing some changes for package_info_plus saw that example app has non-scrollable content, so in landscape mode there is an overflow (see attached screenshot). This PR fixes it along with switching example app to usage of Material 3. Used the same color seed as in share_plus. The only addition is an elevation to AppBar, so it is not white by default. Did the same adjustment to share_plus for consistency.

Before:

After:

Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I titled the PR using Conventional Commits.
• I did not modify the CHANGELOG.md nor the pubspec.yaml files.
• All existing and new tests are passing.
• The analyzer (flutter analyze) does not report any problems on my PR.

Breaking Change

Does your PR require plugin users to manually update their apps to accommodate your change?

• Yes, this is a breaking change (please indicate that with a ! in the title as explained in Conventional Commits).
• No, this is not a breaking change.

[nohli]

Nice