fix #178045: update expansible documentation for default maintainSta…

[koukibadr]

This PR updates the Expansible maintainState documentation in the code, current maintainState default value is set to true while the documentation shows '/// Defaults to false.

Update

• the PR updates the documentation to reflect the maintainState default value without updating the maintainState value which require more investigation and test

Fixes issues/178045

Pre-launch Checklist

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

[gemini-code-assist]

Code Review

This pull request correctly updates the documentation for the maintainState property in the Expansible widget. The documentation previously stated that the default value was false, while the code's default is true. This change aligns the documentation with the implementation, which is a good and necessary fix.

[victorsanni]

Thanks for the change. Sorry I missed this when writing the API docs.

[hannah-hyj]

LGTM