Make humanized size rounding clearer by padding decimals with zeroes

For example, "5 MB" will now be displayed as "5.00 MB" to make the
rounding precision clear, regardless of the value being rounded.

This closes #29611.

core/ustring.cpp

@@ -3246,7 +3246,7 @@ String String::humanize_size(size_t p_size) {
 	int digits = prefix_idx > 0 ? _humanize_digits(p_size / _div) : 0;
 	double divisor = prefix_idx > 0 ? _div : 1;
 
-	return String::num(p_size / divisor, digits) + prefix[prefix_idx];
+	return String::num(p_size / divisor).pad_decimals(digits) + prefix[prefix_idx];
 }
 bool String::is_abs_path() const {