Fix the summarization font

Use the variable width font rather than the OS default and add some
padding (and move around some margins) to prevent italic text from
being truncated on the 'start' edge.

Test: presubmit screenshot tests
Fixes: 425994847
Fixes: 422881504
Flag: android.app.nm_summarization_ui

Change-Id: I5e403186621e7191f9ec3967e66073da2b243865