Block Supports: Output flex-direction row when a viewport override switches a vertical flex layout to horizontal.

[jorgefilipecosta]

Backport of WordPress/gutenberg#82364.

Currently, when a vertical (Stack) flex layout is set to horizontal on the tablet or mobile viewports, the block stays vertical. The viewport rule only outputs the justification and the base flex-direction: column keeps applying. This PR fixes the issue by outputting flex-direction: row when a viewport override switches the orientation to horizontal.

Trac ticket: TBD

Use of AI Tools

AI assistance: Yes
Used for: fix and tests drafted with AI assistance; reviewed and edited by me.

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[talldan]

Thanks, fixes the issue for me on the frontend.