Move SpanUtil into text.span package

Seems like it belongs here.

PiperOrigin-RevId: 295571820

library/core/src/main/java/com/google/android/exoplayer2/text/SpanUtil.java → library/core/src/main/java/com/google/android/exoplayer2/text/span/SpanUtil.java

@@ -13,7 +13,7 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-package com.google.android.exoplayer2.text;
+package com.google.android.exoplayer2.text.span;
 
 import android.text.Spannable;
 import android.text.style.ForegroundColorSpan;

library/core/src/main/java/com/google/android/exoplayer2/text/ttml/TtmlRenderUtil.java

@@ -28,8 +28,8 @@ import android.text.style.StyleSpan;
 import android.text.style.TypefaceSpan;
 import android.text.style.UnderlineSpan;
 import androidx.annotation.Nullable;
-import com.google.android.exoplayer2.text.SpanUtil;
 import com.google.android.exoplayer2.text.span.HorizontalTextInVerticalContextSpan;
+import com.google.android.exoplayer2.text.span.SpanUtil;
 import java.util.Map;
 
 /**

library/core/src/main/java/com/google/android/exoplayer2/text/webvtt/WebvttCueParser.java

@@ -15,7 +15,7 @@
  */
 package com.google.android.exoplayer2.text.webvtt;
 
-import static com.google.android.exoplayer2.text.SpanUtil.addOrReplaceSpan;
+import static com.google.android.exoplayer2.text.span.SpanUtil.addOrReplaceSpan;
 import static java.lang.annotation.RetentionPolicy.SOURCE;
 
 import android.graphics.Color;

library/core/src/test/java/com/google/android/exoplayer2/text/SpanUtilTest.java → library/core/src/test/java/com/google/android/exoplayer2/text/span/SpanUtilTest.java

@@ -13,7 +13,7 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-package com.google.android.exoplayer2.text;
+package com.google.android.exoplayer2.text.span;
 
 import static com.google.common.truth.Truth.assertThat;