Hide share button in portrait mode to save space

[eltos]

Spin-off from #15627 (comment)

Hides the additional share button in portrait mode, where not much space is available. Note that the three dot menu contains an easily accessible share menu with even more features (local share via other app & various nextcloud share options).
In landscape mode there is no change, it is still shown as before (e.g. useful for tablets).

Portrait	Landscape

[kra-mo]

Makes sense from my side, keeping it on landscape is a nice touch :)

We hide it based on the width on the web too anyway.

[github-actions]

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