[ProgressIndicator] Closes #2361 - Allows extending LinearProgressIndicator and CircularProgressIndicator

Resolves #3416

GIT_ORIGIN_REV_ID=7e3b997ae796d047c7c0f381af51397f5c29a1f8
PiperOrigin-RevId: 547902662

Author: ekager

lib/java/com/google/android/material/progressindicator/CircularProgressIndicator.java

@@ -55,7 +55,7 @@
  * developer guidance</a> and <a
  * href="https://material.io/components/progress-indicators/overview">design guidelines</a>.
  */
-public final class CircularProgressIndicator
+public class CircularProgressIndicator
     extends BaseProgressIndicator<CircularProgressIndicatorSpec> {
   public static final int DEF_STYLE_RES =
       R.style.Widget_MaterialComponents_CircularProgressIndicator;

lib/java/com/google/android/material/progressindicator/LinearProgressIndicator.java

@@ -54,7 +54,7 @@
  * developer guidance</a> and <a
  * href="https://material.io/components/progress-indicators/overview">design guidelines</a>.
  */
-public final class LinearProgressIndicator
+public class LinearProgressIndicator
     extends BaseProgressIndicator<LinearProgressIndicatorSpec> {
   public static final int DEF_STYLE_RES = R.style.Widget_MaterialComponents_LinearProgressIndicator;