USWDS - Core: Update comment style for SASS functions

[mejiaj]

Is your feature request related to a problem? Please describe.

Use documentation comments instead of CSS style comments to prevent them from being included in compiled CSS.

Example of commented code seen on compile
#5209

Describe the solution you'd like

For example:

- /*
- ========================================
- General-purpose functions
- ----------------------------------------
- */


+ // ==========================================================================
+ // General-purpose functions
+ // ==========================================================================

- /* ln()
- ----------------------------------------
- */

+ //
+ // ln()
+ // ==========================================================================
+
+ /// Computes an exponent.
+ ///
+ /// @param {number} $value
+ ///   The exponent.
+ /// @return {number} `$value` to the power of 10.

Describe alternatives you've considered

No response

Additional context

Following this style will make it easier to integrate sassdoc.
https://sass-lang.com/documentation/syntax/comments#documentation-comments

Related issue:
#2642

Code of Conduct

• I agree to follow this project's Code of Conduct.
• I checked the current issues for duplicate feature requests.