fix(material/snack-bar): incorrect width at some breakpoints (#26334)

MDC has some built in breakpoints where the snack bar container becomes `min-width: 100%`. They didn't work correctly, because the container wasn't set up to be 100% wide.

Fixes #26290.

(cherry picked from commit 397bd41)

Author: crisbeto

src/material/snack-bar/snack-bar-container.scss

@@ -1,5 +1,4 @@
 @use 'sass:map';
-@use '@angular/cdk';
 @use '@material/snackbar/snackbar' as mdc-snackbar;
 @use '@material/snackbar/snackbar-theme' as mdc-snackbar-theme;
 @use '../core/mdc-helpers/mdc-helpers';
@@ -10,13 +9,28 @@
   @include mdc-snackbar.static-styles($query: mdc-helpers.$mdc-base-styles-without-animation-query);
 }
 
+@mixin _container-min-width {
+  $min-width: mdc-snackbar-theme.$min-width;
+  $mobile-breakpoint: mdc-snackbar-theme.$mobile-breakpoint;
+
+  // The styles weren't included in `static-styles` so we need to add them ourselves.
+  @include mdc-snackbar-theme.min-width(
+    $min-width: $min-width,
+    $mobile-breakpoint: $mobile-breakpoint,
+    $query: mdc-helpers.$mdc-base-styles-query
+  );
+
+  // The MDC `min-width` mixin has a similar breakpoint that sets `min-width: 100%` on the surface
+  // element to make it span the entire viewport, however it ends up collapsing because the
+  // container is `width: auto`. This query ensures that the surface will span the whole viewport.
+  @media (max-width: $mobile-breakpoint), (max-width: $min-width) {
+    width: 100vw;
+  }
+}
+
 .mat-mdc-snack-bar-container {
   @include mdc-helpers.disable-mdc-fallback-declarations {
-    // The styles weren't included in `static-styles` so we need to add them ourselves.
-    @include mdc-snackbar-theme.min-width(
-      mdc-snackbar-theme.$min-width,
-      $query: mdc-helpers.$mdc-base-styles-query
-    );
+    @include _container-min-width;
     @include mdc-snackbar-theme.max-width(
       mdc-snackbar-theme.$max-width,
       $query: mdc-helpers.$mdc-base-styles-query
@@ -60,10 +74,6 @@
   // of positions, so we'll defer logic there.
   position: static;
 
-  @include cdk.high-contrast(active, off) {
-    border: solid 1px;
-  }
-
   // The `mat-mdc-button` and `:not(:disabled)` here are redundant, but we need them to increase
   // the specificity over the button styles that may bleed in from the rest of the app.
   .mat-mdc-button.mat-mdc-snack-bar-action:not(:disabled) {