fix: rename and export color-contrast-variables used in _variables.scss

Author: mrholek

scss/_functions.scss

@@ -2,6 +2,7 @@
 @forward "functions/assert-starts-at-zero";
 @forward "functions/color";
 @forward "functions/color-contrast";
+@forward "functions/color-contrast-variables";
 @forward "functions/contrast-ratio";
 @forward "functions/escape-svg";
 @forward "functions/maps";

scss/_variables.scss

@@ -896,7 +896,7 @@ $btn-active-box-shadow:       inset 0 3px 5px rgba($black, .125) !default;
 $btn-link-color:              var(--#{$prefix}link-color) !default;
 $btn-link-hover-color:        var(--#{$prefix}link-hover-color) !default;
 $btn-link-disabled-color:     $gray-600 !default;
-$btn-link-focus-shadow-rgb:   to-rgb(color.mix(color-contrast($link-color, $color-contrast-dark, $color-contrast-light, $white, $black, $min-contrast-ratio), $link-color, 15%)) !default;
+$btn-link-focus-shadow-rgb:   to-rgb(color.mix(color-contrast-variables($link-color, $color-contrast-dark, $color-contrast-light, $white, $black, $min-contrast-ratio), $link-color, 15%)) !default;
 
 // Allows for customizing button radius independently from global border radius
 $btn-border-radius:           var(--#{$prefix}border-radius) !default;

scss/functions/_color-contrast-variables.scss

@@ -1,9 +1,8 @@
 @use "contrast-ratio" as *;
 
-// Color contrast
-// See https://github.com/twbs/bootstrap/pull/30168
+// We use this function only in variables.scss because recursive imports are not allowed in Sass anymore.
 
-@function color-contrast($background, $color-contrast-dark, $color-contrast-light, $white, $black, $min-contrast-ratio) {
+@function color-contrast-variables($background, $color-contrast-dark, $color-contrast-light, $white, $black, $min-contrast-ratio) {
   $foregrounds: $color-contrast-light, $color-contrast-dark, $white, $black;
   $max-ratio: 0;
   $max-ratio-color: null;