WebView: make notes in docs stand out

This CL rewrites notes to use the 'note' CSS class, to help them stand
out. This isn't every instance of 'note', but it catches the handful
where I think there's a readability benefit to the new format.

This changes a few other non-public notes for the sake of consistency.

Change-Id: Icf62e34a719c79f74e74abdb55f1be42939c2f9e
Fixes: 68324591
Test: make -j40 docs (and manually verify it looks good)