Add backdrop.color to libf3d and a f3d option

[PedroAbreuMaia]

Describe your changes

• Added libf3d option ui.backdrop.color option to control backdrop color.
• Added a CLI option to control it --backdrop-color.
• This option is set black by default.
• Added new tests.

Issue ticket number and link if any

#2861

Checklist for finalizing the PR

• I have performed a self-review of my code
• I have added tests for new features and bugfixes
• I have added documentation for new features
• If it is a modifying the libf3d API, I have updated bindings
• If it is a modifying the .github/workflows/versions.json, I have updated docker_timestamp

Continuous integration

Please write a comment to run CI, eg: \ci fast.
See here for more info.

[mwestphal]

thanks, ill review later today.

[mwestphal]

changes needed

[mwestphal]

• Please resolve discussions if you've adressed them, instead of commenting "Done" :)
• Please avoid merging with master, instead use rebase, and only if needed.

[mwestphal]

\ci fast

[mwestphal]

one last small change, I've also run CI :)

[PedroAbreuMaia]

\ci fast

[mwestphal]

LGTM, lets check CI

[mwestphal]

\ci full

[mwestphal]

this is breaking many tests, it must be changing the default behavior of f3d, which we do not want. Please take a look :)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.15%. Comparing base (d16ba95) to head (5da934b).
⚠️ Report is 23 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2989      +/-   ##
==========================================
+ Coverage   97.12%   97.15%   +0.02%     
==========================================
  Files         208      211       +3     
  Lines       16695    17206     +511     
==========================================
+ Hits        16215    16716     +501     
- Misses        480      490      +10     

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[mwestphal]

Please note the CI failure is not related and caused by a github issue.

[mwestphal]

almost there :)

[mwestphal]

A question about default value

[mwestphal]

one last doc change

[mwestphal]

Thanks for the contribution @PedroAbreuMaia !