fix(material/progress-bar): avoid CSP issues due to buffer dots (#31818)

Currently the way we render the buffer dots in the progress bar is by using a `data:` URL with an inline SVG. The problem with this approach is that it can trigger CSP errors and require users to allow all `data:` URLs, even if they don't use the buffer mode.

These changes work around the issue by rendering the dots using a radial gradient instead.

Fixes #31808.

Author: crisbeto

src/material/progress-bar/progress-bar.scss

@@ -1,7 +1,6 @@
 @use '@angular/cdk';
 @use './m3-progress-bar';
 @use '../core/tokens/token-utils';
-@use '../core/style/vendor-prefixes';
 
 $fallbacks: m3-progress-bar.get-tokens();
 
@@ -104,18 +103,18 @@ $fallbacks: m3-progress-bar.get-tokens();
 }
 
 .mdc-linear-progress__buffer-dots {
-  $mask: "data:image/svg+xml,%3Csvg version='1.1' xmlns='http://www.w3.org/2000/svg' " +
-         "xmlns:xlink='http://www.w3.org/1999/xlink' x='0px' y='0px' " +
-         "enable-background='new 0 0 5 2' xml:space='preserve' viewBox='0 0 5 2' " +
-         "preserveAspectRatio='xMinYMin slice'%3E%3Ccircle cx='1' cy='1' r='1'/%3E%3C/svg%3E";
-
-  @include vendor-prefixes.mask-image(url($mask));
+  $circle-color: token-utils.slot(progress-bar-track-color, $fallbacks);
+  $circle-size: calc(#{token-utils.slot(progress-bar-track-height, $fallbacks)} / 2);
+  background-image: radial-gradient(circle, #{$circle-color} #{$circle-size}, transparent 0);
   background-repeat: repeat-x;
+  background-size: calc(#{$circle-size} * 5);
+  // The `background-position` prevents the animation from jumping around when the progress
+  // changes. Note that we shouldn't invert it in RTL, because the animation direction is reversed.
+  background-position: left;
   flex: auto;
   transform: rotate(180deg);
   animation: mdc-linear-progress-buffering
     calc(250ms * var(--mat-progress-bar-animation-multiplier)) infinite linear;
-  background-color: token-utils.slot(progress-bar-track-color, $fallbacks);
 
   @include cdk.high-contrast {
     background-color: ButtonBorder;