Match lerped values using moreOrLessEquals (#64908)

Several of our tests make use of numbers without an exact floating point
representation (frequently 0.x where x!=5) which, when scaled, also
scale the error. The end result is that some of these tests currently
implicitly rely on an implementation detail of floating point math and
are sensitive to differences in the ~15th decimal place.

This patch reduces the sensitivity of some of these tests, checking
values using `moreOrLessEquals` from the flutter_test package
rather than requiring en exact match.