Implemented QTCANVAS3D_texture_provider extension for creating
a texture object for QQuickItems that implement texture providers.

[ChangeLog][Renderer] Enabled using Qt Quick items as textures.

Change-Id: I947304155734af50c8a21f34292b244bb099702f
Reviewed-by: Tomi Korpipää <tomi.korpipaa@theqtcompany.com>
Reviewed-by: Laszlo Agocs <laszlo.agocs@theqtcompany.com>
Reviewed-by: Topi Reiniö <topi.reinio@digia.com>
Reviewed-by: Pasi Keränen <pasi.keranen@digia.com>