[include-cleaner] Add a signal to down-rank exporting headers

Currently exporter can have same relevance signals as the origin header
when name match signals don't trigger.
This patch introduces a tie braker signal to boost origin headers in
such cases, this is deliberately introduced with lower significance than
public-ness to make sure we still prefer a public-exporter instead of a
private-origin header.

Differential Revision: https://reviews.llvm.org/D154349