For vertex color, we should parse it as long as we have more than 7 elements in the line that starts with `"v "`.

#11270 OBJLoader assigns flat shading if smoothing group is defined as 0 or off. All other values lead to smooth shading

Adjusted to removal of MultiMaterial

This targets separate but logically joined lines (separated by a continuation character, e.g. `\`) and joins them.

OBJLoader: Fix bug that produced geom group and multi-material for objects where the last line is a material change. (#9645)

This was incorrectly used for multi-material even if no faces for the new material were declared.

Fixes #9495

`String.prototype.replace` only targets and replaces the first occurrence of a string. By using a regex with the global flag, all instances of a pattern are replaced.

Inherited material is overwritten if 'usemtl' declaration is encountered after the object starts but prior to next object start.
Exception to this is when faces have been declared to the inherited material, to keep MultiMaterial in sync.

Fixes #8792 and #8871.

* ObjLoader: Implement support for multiple materials inside a geometry/object.
- Tracks material declaration occuring mid face declaration
- If object has multiple materials MultiMaterial is creted and geometry groups are created.
- This approach is better than splitting into separate objects: 1) we are creating as many objects the file defines (correctness) 2) The full geometry would be duplicated into
  two objects, afaik this uploads the geometry multiple times to the GPU (perf, i had test asset that had >400 submeshes with 1-6 geometry groups each).

Fixes #8681 #8640
Updates #8203 (fixes OPs 2. point)

* OBJLoader: Code cleanup and three.js style formatting.

ObjLoader: Ignore silently o/g line declarations that are not followed by any geometry (f) before a new o/g is started. Discussed in #6682.