Experimental.TextureLoader: add returning overloads in TextureLoader
Experimental.TextureLoader: add returning overloads in TextureLoader

The new overloads return the textures instead of passing them via callback,
and makes the API more usable. We can deprecate the old callback overloads.

fusetools/fuselibs-public,kusma/fuselibs-public,kusma/fuselibs-public,fusetools/fuselibs-public,fusetools/fuselibs-public,kusma/fuselibs-public,kusma/fuselibs-public,kusma/fuselibs-public,fusetools/fuselibs-public,fusetools/fuselibs-public,kusma/fuselibs-public,fusetools/fuselibs-public,fusetools/fuselibs-public,kusma/fuselibs-public