Support high contrast colors

[alexey1312]

Solution for this issue

[subdan]

• Add information about supporting high contrast colors in the Design requirements and Features section.
• Add unit tests

[subdan]

1. Fix typo hight → high
2. Fix issue I point in the comment about dark appearance.
3. Add unit tests for XcodeColorExporter which checks exporting high contrast colors for useSingleFile is true and false.
4. I tried to run FigmaExport for Example project and it fails to export with the following error: Bad asset name.... You must fix this issue.

[alexey1312]

1 - Fix typo hight → high ✅
2 - Fix issue I point in the comment about dark appearance. ✅
3 - Add unit tests for XcodeColorExporter which checks exporting high contrast colors for useSingleFile is true and false.
It seems that testing useSingleFile in XcodeColorExporter is not very correct, since different areas of responsibility.
I think we need to write tests on the ColorLoader, but for this it needs to be refactored.
I checked in Playgrounds, the filter for useSingleFile works correctly. ✅
4 - I tried to run FigmaExport for Example project and it fails to export with the following error: Bad asset name.... You must fix this issue. ✅

[subdan]

Method checkSubtracting can generate darkAssetsNotFoundInLightPalette error only but you specified light and light high contrast colors.

[subdan]

Thanks for the PR, @alexey1312! I've published a new version of FigmaExport with this feature.

[alexey1312]

Thanks for the code review, @subdan ! 🙏