Add TestApi to WM refresh rate param.

Bug: 276803096
Test: See CTS change
Change-Id: I2889d094c1ae7a9fb3dd5ad89789aba916f91b20

core/api/test-current.txt

@@ -3568,6 +3568,8 @@ package android.view {
     field public static final int ACCESSIBILITY_TITLE_CHANGED = 33554432; // 0x2000000
     field public static final int FLAG_SLIPPERY = 536870912; // 0x20000000
     field public CharSequence accessibilityTitle;
+    field public float preferredMaxDisplayRefreshRate;
+    field public float preferredMinDisplayRefreshRate;
     field public int privateFlags;
   }
 

core/java/android/view/WindowManager.java

@@ -3755,6 +3755,7 @@ public interface WindowManager extends ViewManager {
          * This value is ignored if {@link #preferredDisplayModeId} is set.
          * @hide
          */
+        @TestApi
         public float preferredMinDisplayRefreshRate;
 
         /**
@@ -3763,6 +3764,7 @@ public interface WindowManager extends ViewManager {
          * This value is ignored if {@link #preferredDisplayModeId} is set.
          * @hide
          */
+        @TestApi
         public float preferredMaxDisplayRefreshRate;
 
         /** Indicates whether this window wants the HDR conversion is disabled. */