Use fluent assertions

Gives a bit more information upon failures

PiperOrigin-RevId: 451882968

testutils/src/main/java/com/google/android/exoplayer2/testutil/FakeExtractorInput.java

@@ -100,8 +100,8 @@ public final class FakeExtractorInput implements ExtractorInput {
    * @param position The position to set.
    */
   public void setPosition(int position) {
-    assertThat(0 <= position).isTrue();
-    assertThat(position <= data.length).isTrue();
+    assertThat(position).isAtLeast(0);
+    assertThat(position).isAtMost(data.length);
     readPosition = position;
     peekPosition = position;
   }