Add prefix to ImageDecoder.Allocator

Bug: 73788928
Test: No change in behavior; no new tests

This will allow the generated JavaDocs to include these in setAllocator.

Change-Id: Icd109ddf45e8809da1a0980924a6f4feccefcac2

graphics/java/android/graphics/ImageDecoder.java

@@ -758,8 +758,9 @@ public final class ImageDecoder implements AutoCloseable {
 
     /** @hide **/
     @Retention(SOURCE)
-    @IntDef({ ALLOCATOR_DEFAULT, ALLOCATOR_SOFTWARE, ALLOCATOR_SHARED_MEMORY,
-              ALLOCATOR_HARDWARE })
+    @IntDef(value = { ALLOCATOR_DEFAULT, ALLOCATOR_SOFTWARE,
+              ALLOCATOR_SHARED_MEMORY, ALLOCATOR_HARDWARE },
+              prefix = {"ALLOCATOR_"})
     public @interface Allocator {};
 
     /**