LDrawLoader: remove separateobjects flag

[gkjohnson]

Related issue: #23139 (comment)

Description

• Removes the LDrawLoader.separateObjectst flag from both the class and the example -- this can be added back at a future time if needed.
• This PR also moved the inversion of primitive winding order if the transformation matrix is scale inverted out of objectParse, as well.
• Moves the parseVector function to LineParser.getVector.

Next up will be rethinking the "main" color used when loading a sub file so the parsed contents of individual files can be more easily cached.

[mrdoob]

Thanks!