sharing: Allow dialogs to have smaller width

Reduce margins on either side, and allow the texts to be
wrapped early, so that it works well on smaller screens
11 jobs for wip/sadiq/sharing-panel in 3 minutes and 39 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Build
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  Test
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passed #364165
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flatpak
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ppc64le
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tsan
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  Review
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review
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