fix(material-experimental/mdc-slider): code review changes

* use @use instead of @import for @material/slider styles
* make tooltip color change when in dark theme
* add underscore to custom-slider-color to ensure it doesn't get exported

Author: wagnermaciel

src/material-experimental/mdc-slider/_slider-theme.scss

@@ -1,22 +1,26 @@
-@import '@material/slider/slider';
+@use '@material/slider/slider' as mdc-slider;
 @import '@material/slider/slider-theme';
 @import '../mdc-helpers/mdc-helpers';
 @import '../../material/core/ripple/ripple';
 
 @mixin mat-mdc-slider-color($config-or-theme) {
   $config: mat-get-color-config($config-or-theme);
   @include mat-using-mdc-theme($config) {
-    @include without-ripple($query: $mat-theme-styles-query);
+    @include mdc-slider.without-ripple($query: $mat-theme-styles-query);
 
     .mat-mdc-slider {
       &.mat-primary, &.mat-accent, &.mat-warn {
+        $is-dark: map-get($config, is-dark);
+        $indicator-color: if($is-dark, white, black);
+        $indicator-text-color: if($is-dark, black, white);
+
         @include value-indicator-color(
-          $color: #000,
+          $color: $indicator-color,
           $opacity: 0.6,
           $query: $mat-theme-styles-query
         );
         @include value-indicator-text-color(
-          $color: on-primary,
+          $color: $indicator-text-color,
           $query: $mat-theme-styles-query
         );
         @include tick-mark-active-color(
@@ -29,15 +33,15 @@
       }
 
       &.mat-primary {
-        @include custom-slider-color(primary);
+        @include _custom-slider-color(primary);
       }
 
       &.mat-accent {
-        @include custom-slider-color(secondary);
+        @include _custom-slider-color(secondary);
       }
 
       &.mat-warn {
-        @include custom-slider-color(error);
+        @include _custom-slider-color(error);
       }
     }
   }
@@ -71,7 +75,7 @@
   }
 }
 
-@mixin custom-slider-color($color) {
+@mixin _custom-slider-color($color) {
   @include thumb-color(
     $color-or-map: (
       default: $color,

src/material-experimental/mdc-slider/slider.scss

@@ -1,7 +1,7 @@
-@import '@material/slider/slider';
+@use '@material/slider/slider' as mdc-slider;
 @import '../mdc-helpers/mdc-helpers';
 
-@include without-ripple($query: $mat-base-styles-query);
+@include mdc-slider.without-ripple($query: $mat-base-styles-query);
 
 .mdc-slider {
   display: block;