Overview

Add barrierDismissible, barrierColor and barrierLabel parameters to showDatePicker, showTimePicker and showAboutDialog which calls showDialog internally.
We can change these parameters with showDialog and Dialog widgets (like DatePickerDialog, TimePickerDialog or AboutDialog) directly. But, I think it is prefer to provide interfaces same as showDialog to keep application wide unified looks if it is used internally.

Fixes #130971

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.
• All existing and new tests are passing.

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