docs: added units to <webview>.print() pageSize option

[mkiki01]

Description of Change

Closes #33097.

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• PR description included and stakeholders cc'd
• npm test passes
• relevant documentation is changed or added
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[ckerr]

LGTM, but I think this would be superseded by #33654 ?

CC @codebytere

[jkleinsc]

@ckerr #33654 modifies ``.printToPDF(options)and this documentation change is for.print(options)`

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