Suppress warnings in preparation for Checker Framework 3.2.0 upgrade.

In particular, replace @SuppressWarnings("initialization") with
@SuppressWarnings("nullness"); see
https://github.com/typetools/checker-framework/issues/3212.

More information: go/checker-lsc

Tested:
    TAP train for global presubmit queue
    http://test/OCL:304697666:BASE:304680497:1585968008044:f0c4fd6c
PiperOrigin-RevId: 304751415

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

@@ -31,7 +31,7 @@ public abstract class SimpleSubtitleDecoder extends
   private final String name;
 
   /** @param name The name of the decoder. */
-  @SuppressWarnings("initialization:method.invocation.invalid")
+  @SuppressWarnings("nullness:method.invocation.invalid")
   protected SimpleSubtitleDecoder(String name) {
     super(new SubtitleInputBuffer[2], new SubtitleOutputBuffer[2]);
     this.name = name;

library/core/src/main/java/com/google/android/exoplayer2/trackselection/TrackSelectionParameters.java

@@ -47,7 +47,7 @@ public class TrackSelectionParameters implements Parcelable {
      *
      * @param context Any context.
      */
-    @SuppressWarnings({"deprecation", "initialization:method.invocation.invalid"})
+    @SuppressWarnings({"deprecation", "nullness:method.invocation.invalid"})
     public Builder(Context context) {
       this();
       setPreferredTextLanguageAndRoleFlagsToCaptioningManagerSettings(context);