Add AndroidInAppWebViewOption for using Hybrid Composition

[tneotia]

Connection with issue(s)

Add the ability to dynamically enable/disable Hybrid Composition by means of an AndroidInAppWebViewOption.

Testing and Review Notes

Steps:

• Flutter version v1.20+.
• Set useHybridComposition to true in example/lib/in_app_webview_example.screen.dart (at line 92 add):

android: AndroidInAppWebViewOptions(
    useHybridComposition: true,
)

• Install Google gboard input method, and install chinese pinyin or chuyin input method, and launch InAppWebView with some website that needs some input.
• Focus on the text field and see if it's possible to switch to pinyin input method in gboard (should be possible).
• Set useHybridComposition to false in example/lib/in_app_webview_example.screen.dart.
• Focus on the text field and see if it's possible to switch to pinyin input method in gboard (should not be possible).

To Do

• double check the original issue to confirm it is fully satisfied
• add testing notes and screenshots in PR description to help guide reviewers
• request the "UX" team perform a design review (if/when applicable)

[tneotia]

@plateaukao Don't know how it works if I would like this commit to get merged onto the branch you pushed to flutter_inappwebview, but I tried it anyways. Let me know if there is a different way I should do this.

[plateaukao]

LGTM!