fixed_decimal: clarify documentation for position sign in padding fun…

…ctions (#5243)

Example:
`pad_start` documentation states that "Negative numbers have no effect".
This is ambiguous between the number being formatted and the position
number passed as an argument.

Resolve this and other similar instances. Example: "Negative position
numbers have no effect"

utils/fixed_decimal/src/decimal.rs

@@ -1024,7 +1024,7 @@ impl FixedDecimal {
 
     /// Returns this number padded with leading zeros on a particular position.
     ///
-    /// Negative numbers have no effect.
+    /// Negative position numbers have no effect.
     ///
     /// Also see [`FixedDecimal::with_max_position()`].
     ///
@@ -1050,7 +1050,7 @@ impl FixedDecimal {
 
     /// Pads this number with leading zeros on a particular position.
     ///
-    /// Negative numbers have no effect.
+    /// Negative position numbers have no effect.
     ///
     /// Also see [`FixedDecimal::set_max_position()`].
     ///
@@ -1091,7 +1091,7 @@ impl FixedDecimal {
     /// Returns this number padded with trailing zeros on a particular (negative) position.
     /// Will truncate zeros if necessary, but will not truncate other digits.
     ///
-    /// Positive numbers have no effect.
+    /// Positive position numbers have no effect.
     ///
     /// Also see [`FixedDecimal::trunced()`].
     ///
@@ -1120,7 +1120,7 @@ impl FixedDecimal {
     /// Pads this number with trailing zeros on a particular (non-positive) position. Will truncate
     /// trailing zeros if necessary, but will not truncate other digits.
     ///
-    /// Positive numbers have no effect.
+    /// Positive position numbers have no effect.
     ///
     /// Also see [`FixedDecimal::trunc()`].
     ///