BLI_math: add floor_power_of_10, ceil_power_of_10

Add utility functions to get the floor/ceiling of a float value
to the next power of 10.

source/blender/blenlib/BLI_math_base.h

@@ -219,6 +219,9 @@ MINLINE unsigned int round_db_to_uint_clamp(double a);
 int pow_i(int base, int exp);
 double double_round(double x, int ndigits);
 
+float floor_power_of_10(float f);
+float ceil_power_of_10(float f);
+
 #ifdef BLI_MATH_GCC_WARN_PRAGMA
 #  pragma GCC diagnostic pop
 #endif