[Material] Ensure banner reads banner theme's leading padding property

[rami-a]

Description

The banner theme's padding param was being used instead of leadingPadding. This change fixes that bug.

Related Issues

Closes #62128

Tests

I updated the existing banner theme tests to adequately catch this bug

Checklist

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Breaking Change

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[willlarche]

LGTM

[HansMuller]

LGTM