Simplify the applyOpacity helper function

This function only has a single call-site (if we ignore the unit-tests), where the colors are split into separate parameters.
Given that all the color components are modified in the exact same way, it seems easier (and shorter) to pass the colors as-is to `applyOpacity` and have it use `Array.prototype.map()` instead.

Author: Snuffleupagus

src/display/display_utils.js

@@ -794,13 +794,10 @@ class CSSConstants {
   }
 }
 
-function applyOpacity(r, g, b, opacity) {
+function applyOpacity(color, opacity) {
   opacity = MathClamp(opacity ?? 1, 0, 1);
   const white = 255 * (1 - opacity);
-  r = Math.round(r * opacity + white);
-  g = Math.round(g * opacity + white);
-  b = Math.round(b * opacity + white);
-  return [r, g, b];
+  return color.map(c => Math.round(c * opacity + white));
 }
 
 function RGBToHSL(rgb, output) {

test/unit/display_utils_spec.js

@@ -323,7 +323,7 @@ describe("display_utils", function () {
       ctx.globalAlpha = 0.8;
       ctx.fillRect(0, 0, 1, 1);
       const [r, g, b] = ctx.getImageData(0, 0, 1, 1).data;
-      expect(applyOpacity(123, 45, 67, ctx.globalAlpha)).toEqual([r, g, b]);
+      expect(applyOpacity([123, 45, 67], ctx.globalAlpha)).toEqual([r, g, b]);
     });
   });
 

web/comment_manager.js

@@ -132,7 +132,7 @@ class CommentManager {
     return this.#hasForcedColors
       ? null
       : findContrastColor(
-          applyOpacity(...color, opacity ?? 1),
+          applyOpacity(color, opacity ?? 1),
           CSSConstants.commentForegroundColor
         );
   }