MTLLoader: Support for texture parameters (#9311)

* MTLLoader: Support for texture parameters

 -s u v w for scale (w is ignored)
 -o u v w for offset (w is ignored)
 -bm s for bumpmap scale

* Fix positional argument to get bumpmap scale

* Trim texture url to prevent trailing spaces

* Fix calls to getTextureParams (pass material parameters)

* Add missing 'var's