ohos: Implement QWebViewSettings support

Implement QWebViewSettings support for the OHOS WebView backend.

The following web attributes are now supported and synchronized with the
native Web component:

- LocalStorageEnabled
- JavaScriptEnabled
- AllowFileAccess
- LocalContentCanAccessFileUrls

This change requires qtbase change
3a8257fb92d59a5ec537eb600f30e2a563f08bdc, which exposes the underlying
Web component needed to apply these settings.

Task-number: QTBUG-146838
Pick-to: 6.12
Change-Id: I91cded8977a95f71c141bd748d3ce1899aff9848
Reviewed-by: Liang Qi <liang.qi@qt.io>
Reviewed-by: Zbigniew Chyla <zbigniew.chyla@qt.io>