Improve Command Palette on mobile

[janfaracik]

Some issues with Command Palette (and other inputs) on mobile (especially iOS...)

• If an inputs font size is smaller than 16px the browser zooms in automatically
• Accidentally had vw instead of vh for a max-height and that caused the dialog to be cut off on portrait devices
• Width issues (didn't take up the full width of the phone)
• Command Palette could look a little odd due to how vh is handled, changing to dvh fixes this

Before

Large image

After

Large image

Testing done

• Tried in a simulator
• Desktop works as before

Proposed changelog entries

• N/A

Proposed upgrade guidelines

N/A

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Desired reviewers

@jenkinsci/sig-ux

Before the changes are marked as ready-for-merge:

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[timja]

LGTM, tested locally
/label ready-for-merge

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This PR is now ready for merge, after ~24 hours, we will merge it if there's no negative feedback.

Thanks!