Add STL to Assemblys export formats

[qwelyt]

Turn the assembly into a compound and use Shapes export method to export the assembly. This way the export function does not need to be duplicated, and it is what users have been doing manually to get their objects.

Should solve https://github.com/CadQuery/cadquery/issues/965

[codecov[bot]]

Codecov Report

Merging #1101 (304aaea) into master (8ddad3b) will increase coverage by 0.00%. The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #1101   +/-   ##
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  Coverage   94.01%   94.01%           
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  Files          26       26           
  Lines        5410     5412    +2     
  Branches      918      919    +1     
=======================================
+ Hits         5086     5088    +2     
  Misses        193      193           
  Partials      131      131           

Impacted Files	Coverage Δ
cadquery/assembly.py	96.56% <100.00%> (+0.02%)	:arrow_up:

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[SDI8]

Shouldn't all of the "shape-formats" be supported then (and not just STL)? This situation is very similar to what is happening with Workplanes in exporters.export, where any Workplane gets converted to a compound first. You could achieve similar functionality to your proposal by allowing Assemblies in exporters.export - although I'm not in a position to foresee all issues that that could entail.

[jmwright]

@lorenzncode @adam-urbanczyk Any thoughts on this?

[adam-urbanczyk]

STL has been discussed already. It does not support all the features of assy (color), but OK popular request and whatnot. -1 for other formats though.

[lorenzncode]

I wasn't sure if the discussion in #965 had concluded. Regarding the use of such an STL, it may be that the user wants to access the solver functionality for a particular part. A user on Discord mentioned this approach, and asked "Am I misusing Assembly?".

[adam-urbanczyk]

Should I merge @jmwright @lorenzncode ?

[jmwright]

+1

[lorenzncode]

+1

[adam-urbanczyk]

Thanks @qwelyt !