Move GrpcStatusTest under servicetalk-grpc-api/src (#2052)

Motivation:

Existing `GrpcStatusTest` is located outside of the `src` folder. As the
result, `servicetalk-grpc-api` module does not recognize it.

Modifications:

- Move `GrpcStatusTest` under `src`;
- Fix pmd errors;

Result:

Gradle can run `GrpcStatusTest`.

servicetalk-grpc-api/test/java/io/servicetalk/grpc/api/GrpcStatusTest.java → servicetalk-grpc-api/src/test/java/io/servicetalk/grpc/api/GrpcStatusTest.java

@@ -19,38 +19,38 @@
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
 
-public class GrpcStatusTest {
+class GrpcStatusTest {
 
     @Test
-    public void testGrpcStatusFromIntCodeValue() {
+    void testGrpcStatusFromIntCodeValue() {
         final GrpcStatus grpcStatus = GrpcStatus.fromCodeValue(0);
         assertEquals(GrpcStatusCode.OK, grpcStatus.code());
     }
 
     @Test
-    public void testGrpcStatusFromStringCodeValue() {
+    void testGrpcStatusFromStringCodeValue() {
         final GrpcStatus grpcStatus = GrpcStatus.fromCodeValue("0");
         assertEquals(GrpcStatusCode.OK, grpcStatus.code());
     }
 
     @Test
-    public void testGrpcStatusUnknownFromIntCodeValue() {
+    void testGrpcStatusUnknownFromIntCodeValue() {
         int unknownCode = 255;
         final GrpcStatus grpcStatus = GrpcStatus.fromCodeValue(unknownCode);
         assertEquals(GrpcStatusCode.UNKNOWN, grpcStatus.code());
         assertEquals("Unknown code: " + unknownCode, grpcStatus.description());
     }
 
     @Test
-    public void testGrpcStatusUnknownFromStringCodeValue() {
+    void testGrpcStatusUnknownFromStringCodeValue() {
         final String unknownCode = "255";
         final GrpcStatus grpcStatus = GrpcStatus.fromCodeValue(unknownCode);
         assertEquals(GrpcStatusCode.UNKNOWN, grpcStatus.code());
         assertEquals("Unknown code: " + unknownCode, grpcStatus.description());
     }
 
     @Test
-    public void testGrpcStatusUnknownFromUnparsableStringCodeValue() {
+    void testGrpcStatusUnknownFromUnparsableStringCodeValue() {
         final String unknownCode = "1f";
         final GrpcStatus grpcStatus = GrpcStatus.fromCodeValue(unknownCode);
         assertEquals(GrpcStatusCode.UNKNOWN, grpcStatus.code());