When a block container has `clear` set and some clearance is applied,
that clearance prevents margins from adjoining and therefore resets
the margin state. But when a floating box has `clear` set, that
clearance only goes between floating boxes so should not reset margin
state. BlockFormattingContexts already do that correctly, and this PR
changes InlineFormattingContext to do the same.
Fixes#1462; adds reduced input from that issue as test.
