fix(material/core): custom system-level variable prefix not used in some mixins

Fixes that the `system-level-colors` and `system-level-typography` mixins weren't using the `system-variables-prefix` passed in by the user.

Note: a bit of a gotcha here is that we need to store two separate prefixes, because in theory the user can pass different prefixes into `color` and `typography`.

Fixes #29504.

Author: crisbeto

src/material/core/theming/_definition.scss

@@ -55,6 +55,7 @@ $theme-version: 1;
         neutral-variant: map.get($primary, neutral-variant),
         error: map.get($primary, error),
       ),
+      color-system-variables-prefix: $system-variables-prefix,
       color-tokens: m3-tokens.generate-color-tokens(
           $type, $primary, $tertiary, map.get($primary, error), $system-variables-prefix)
     )
@@ -88,6 +89,7 @@ $theme-version: 1;
         medium: $medium,
         regular: $regular,
       ),
+      typography-system-variables-prefix: $system-variables-prefix,
       typography-tokens: m3-tokens.generate-typography-tokens(
           $brand, $plain, $bold, $medium, $regular, $system-variables-prefix)
     )

src/material/core/tokens/_m3-tokens.scss

@@ -135,7 +135,8 @@ $_cached-token-slots: null;
   );
 
   $type: map.get($theme, _mat-theming-internals-do-not-access, theme-type);
-  $system-variables-prefix: map.get($theme, system-variables-prefix) or sys;
+  $system-variables-prefix: map.get($theme, _mat-theming-internals-do-not-access,
+    color-system-variables-prefix) or sys;
   $primary: map.merge(map.get($palettes, primary), $base-palettes);
   $tertiary: map.merge(map.get($palettes, tertiary), $base-palettes);
   $error: map.get($palettes, error);
@@ -160,7 +161,8 @@ $_cached-token-slots: null;
   $bold: map.get($font-definition, bold);
   $medium: map.get($font-definition, medium);
   $regular: map.get($font-definition, regular);
-  $system-variables-prefix: map.get($theme, system-variables-prefix) or sys;
+  $system-variables-prefix: map.get($theme, _mat-theming-internals-do-not-access,
+    typography-system-variables-prefix) or sys;
   $ref: (
     md-ref-typeface: _generate-ref-typeface-tokens($brand, $plain, $bold, $medium, $regular)
   );