Add non-templated versions of get[Static]ObjectField()

Ideally the getStaticObjectField() and getObjectField() methods, that
take a signature, should never have been templated. Removing the
templated versions now will cause ABI breakage, so the only solution
is to add new non-templated versions.

Change-Id: I2f6e9f259b7bc511ef5bcaeb8a2077b0f267b8c8
Reviewed-by: BogDan Vatra <bogdan@kde.org>
Add non-template version of QAndroidJniObject::object()

In many cases we just want the jobject, this removes the need
to add the template type.

Change-Id: Iac5d8eab2b784908201baa8a05b126b4e7e5c86f
Reviewed-by: BogDan Vatra <bogdan@kde.org>