Android: add support for various url schemes.

Android WebView does not handle schemes by default, such
as mailto:, geo:, and others, but will instead show an
"ERR_UNKNOWN_URL_SCHEME" error. This patch fixes it by
starting ACTION_VIEW Intent for specified scheme, meanwhile
showing the same "ERR_UNKNOWN_URL_SCHEME" error page for
invalid cases as before.

[ChangeLog][Android] Added support for various url schemes.

Taks-number: QTBUG-53736
Change-Id: Ib569ec1598f76f823b2293446ea4e513764ef1fa
Reviewed-by: Christian Stromme <christian.stromme@qt.io>