Use only lower floats for Vector3 dot and equality

Use only lower floats for Vector3 dot and equality

For both dot product and comparisons that produce a boolean result, we need to use only the lower 3 floats. The bug was exposed by a case where the result of a call was being used in one of these operations without being stored to a local (which would have caused the upper bits to be cleared).

Fix dotnet/coreclr#8220

Commit migrated from https://github.com/dotnet/coreclr/commit/0403e4d81f67a9abe61bf8637deff85b971381b7