[ProgressIndicator] Simplify flat linear indicator drawing logic

Resolves material-components#5059
Resolves material-components#5060
Resolves material-components#5061
Resolves material-components#5057

Author: pubiqq

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

@@ -186,7 +186,7 @@ protected static class ActiveIndicator {
   }
 
   /** An entity class for a point on a path, with the support of fundamental operations. */
-  protected class PathPoint {
+  protected static class PathPoint {
     // The vector to the position of the point.
     float[] posVec = new float[2];
     // The tangent vector of this point on a path. The length is not guaranteed.