Using relative threshold for floats in mesh comparison

Changes the threshold comparison from absolute to relative.
Removes threshold for MLoopCol comparison.

Adds a compare relative threshold function.

Reviewed By: JacquesLucke

Differential Revision: https://developer.blender.org/D12273

source/blender/blenlib/BLI_math_base.h

@@ -172,6 +172,9 @@ MINLINE size_t clamp_z(size_t value, size_t min, size_t max);
 
 MINLINE int compare_ff(float a, float b, const float max_diff);
 MINLINE int compare_ff_relative(float a, float b, const float max_diff, const int max_ulps);
+MINLINE bool compare_threshold_relative(const float value1,
+                                        const float value2,
+                                        const float thresh);
 
 MINLINE float signf(float f);
 MINLINE int signum_i_ex(float a, float eps);