Inspector: Make default float step configurable

Also allow lifting the decimal step formatting with a hint range step
of 0. A new `range_step_decimals()` is added for this to avoid breaking
compatibility on the general purpose `step_decimals()` (which still
returns 0 for an input step of 0).

Supersedes #25470.
Partial fix for #18251.

core/math/math_funcs.cpp

@@ -79,6 +79,15 @@ int Math::step_decimals(double p_step) {
 	return 0;
 }
 
+// Only meant for editor usage in float ranges, where a step of 0
+// means that decimal digits should not be limited in String::num.
+int Math::range_step_decimals(double p_step) {
+	if (p_step < 0.0000000000001) {
+		return 16; // Max value hardcoded in String::num
+	}
+	return step_decimals(p_step);
+}
+
 double Math::dectime(double p_value, double p_amount, double p_step) {
 	double sgn = p_value < 0 ? -1.0 : 1.0;
 	double val = Math::abs(p_value);