Make LTE_FLOAT a strict weak order.

Make LTE_FLOAT a strict weak order.
Bug: 5327776

Currently LTE_FLOAT isn't even a valid partial order, let alone
a strict weak order as needed by binary search.  Consequently,
KeyedVectors with keys whose types have operator< using LTE_FLOAT
sometimes find the wrong values!

This problem affects several graphics caches including the
TextLayoutCache.

(This is still not a total order because NaNs are not comparable
but hopefully we don't ever search for NaNs this way!)

Change-Id: Ic447a34c7d87f681ee81538f22a0937a039072dd