docs: update FlutterTexture platform note

[Foesa-yyx]

Summary

• Update RTC Flutter VideoViewController useFlutterTexture notes to include Android.
• Sync the same change in zh-CN and en-US DITA sources for VideoViewController, VideoViewControllerBase, and the constructor API page.
• This corresponds to the already merged shengwang-doc-source HTML PR: https://github.com/AgoraIO/shengwang-doc-source/pull/2026

Validation

• xmllint --noout on all 6 edited DITA files
• git diff --check
• Regenerated zh-CN target DITA to /tmp and verified the 3 target notes include Android
• Regenerated en-US target DITA to /tmp and verified the 3 target notes include Android