On aarch64 and when computing the perpendicular distance, we need to
avoid the fmsub (Fused Multiply-Subtract) because it can return
slightly different precision results when evaluating expressions
like
  x = a - (b * c)
such as we did (before this patch) in perpendicular-distance.  Instead,
we now store the result of the multiplication (b * c) and then subtract
it from a which avoids (in all build types) fmsub.

This error occurs because the C++ standard allows implementations to
use higher precision throughout calculations before storing to the destination
type.  This can allow for differences in the final result if using higher
precision meaningfully changes intermediate values which is what happened in
our case.  By breaking the operation into two, we prevent the use case where
fmsub applies, even for optimized builds under our current build flags
configuration.

See also
  https://github.com/dotnet/runtime/issues/64591
  https://stackoverflow.com/questions/51124436/strange-issue-with-floating-point-accuracy-on-arm64