fix: Avoid empty classes/styled elements

[kurtdoherty]

Linaria 0.7.0 does not play nicely with empty classes/styled elements, sometimes throwing build errors like [wyw-in-js] Cannot use 'in' operator to search for 'initialCode' in undefined. There is an issue raised and a PR to fix it, but it remains unmerged.

This PR adds a CSS comment to all currently empty classes/styled elements. This appears to avoid the build issues, though given the build issues are intermittent anyway, it's hard to know if this will stand up over time.

[rpt-uk-github]

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[codacy-production]

Coverage summary from Codacy

See diff coverage on Codacy

Coverage variation	Diff coverage
Report missing for 3ea38231	✅ 100.00%

Coverage variation details

	Coverable lines	Covered lines	Coverage
Common ancestor commit (3ea3823)	Report Missing	Report Missing	Report Missing
Head commit (f846215)	8041	7317	91.00%

Coverage variation is the difference between the coverage for the head and common ancestor commits of the pull request branch: <coverage of head commit> - <coverage of common ancestor commit>

Diff coverage details

	Coverable lines	Covered lines	Diff coverage
Pull request (#647)	24	24	100.00%

Diff coverage is the percentage of lines that are covered by tests out of the coverable lines that the pull request added or modified: <covered lines added or modified>/<coverable lines added or modified> * 100%

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