Indicate that some FrameProcessor methods can be called on any thread

The FrameProcessor is created on the GL thread, but:
- setInputFrameInfo() is currently called from the playback thread.
- release() is currently called from the transformer internal thread.

PiperOrigin-RevId: 501035719

library/common/src/main/java/com/google/android/exoplayer2/util/FrameProcessor.java

@@ -137,6 +137,8 @@ public interface FrameProcessor {
    *
    * <p>The caller should update {@link FrameInfo#streamOffsetUs} when switching input streams to
    * ensure that frame timestamps are always monotonically increasing.
+   *
+   * <p>Can be called on any thread.
    */
   void setInputFrameInfo(FrameInfo inputFrameInfo);
 
@@ -216,6 +218,8 @@ public interface FrameProcessor {
    * ignored.
    *
    * <p>This method blocks until all resources are released or releasing times out.
+   *
+   * <p>Can be called on any thread.
    */
   void release();
 }