feat: provide hook for formatting tokens internally

Author: wagnermaciel

src/material-experimental/theming/_format-tokens.scss

@@ -0,0 +1,5 @@
+// DO NOT REMOVE
+// This function is used internally.
+@function format($systems) {
+  @return $systems;
+}

src/material-experimental/theming/_m3-tokens.scss

@@ -5,6 +5,7 @@
 @use '@material/tokens/v0_161' as mdc-tokens;
 @use './m3-density';
 @use './custom-tokens';
+@use './format-tokens';
 
 // TODO(mmalerba): Split up this file into smaller pieces.
 
@@ -500,6 +501,10 @@
   ), $systems);
   $exclude-hardcoded: not $include-non-systemized;
 
+  // DO NOT REMOVE
+  // This function is used internally.
+  $systems: format-tokens.format($systems);
+
   // TODO(mmalerba): Refactor this to not depend on the legacy theme when moving out of
   //  material-experimental. This is a hack for now because there is no good way to get the token
   //  slots in material-experimental without exposing them all from material.