Fix CSG Union Color Loss

[joeng03]

Description

Fixes #227

As described in the issue, the union operation does not preserve the color of one of the solids when they are non-intersecting. Upon inspection of the JSCAD code, I realized that there is a separate function to handle non-intersecting unions, and the toPolygons function was not called with the option of preserving the individual colors of a polygon using the boolean parameter colorizePolygons. This has been rectified in this PR.

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

Running the snippet provided in #227

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules