[webview_flutter] Enable zoom in android devices.

[rodruiz]

Enable zoom in android devices.

Pre-launch Checklist

• The title of the PR starts with the name of the plugin surrounded by square brackets, e.g. [shared_preferences]
• 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 and the C++, Objective-C, Java style guides.
• I listed at least one issue that this PR fixes in the description above.
• I added new tests to check the change I am making or feature I am adding, or Hixie said the PR is test exempt.
• I updated pubspec.yaml with an appropriate new version according to the pub versioning philosophy.
• I updated CHANGELOG.md to add a description of the change.
• I updated/added relevant documentation (doc comments with ///).
• I signed the CLA.
• All existing and new tests are passing.

If you need help, consider asking for advice on the #hackers-new channel on Discord.

[stuartmorgan-g]

Thanks for the contribution! You’ve checked boxes in the PR checklist above that are not reflected in this PR, so I’m assuming this is a work in progress and am marking it as a Draft. Please review the checklist, updating the PR as appropriate, and when the checklist reflects the state of the PR as posted please feel free to mark it as ready for review.

[LongXiangGuo]

The note format is not correctly.

Suggested change

	// // It loads the WebView with the attributes defined in the meta tag of the webpage.
	// It loads the WebView with the attributes defined in the meta tag of the webpage.

[Hixie]

I'm going to close this since it's marked as a draft but hasn't been touched in a few months; please don't hesitate to open a new PR when ready. Thanks!