Provide default fragment(String) override for all request types (#2626

)

Motivation:

Even though `HttpRequestMetaData#fragment()` has default implementation,
because all request types override it with different return type, we
must provide default implementations for these overrides too. Otherwise,
the code is not backward compatible.

Modifications:

- Add `default` implementation for `fragment(String)` in
`HttpRequest`, `StreamingHttpRequest`, `BlockingStreamingHttpRequest`;

Result:

Request interfaces are backward compatible.

servicetalk-http-api/src/main/java/io/servicetalk/http/api/BlockingStreamingHttpRequest.java

@@ -294,7 +294,10 @@ default <T> BlockingStreamingHttpRequest transform(TrailersTransformer<T, Buffer
     BlockingStreamingHttpRequest version(HttpProtocolVersion version);
 
     @Override
-    BlockingStreamingHttpRequest fragment(@Nullable String fragment);
+    default BlockingStreamingHttpRequest fragment(@Nullable String fragment) {
+        throw new UnsupportedOperationException("BlockingStreamingHttpRequest#fragment(String) is not supported by " +
+                getClass());
+    }
 
     @Deprecated
     @Override

servicetalk-http-api/src/main/java/io/servicetalk/http/api/HttpRequest.java

@@ -137,7 +137,10 @@ default <T> HttpRequest payloadBody(T pojo, HttpSerializer<T> serializer) {
     HttpRequest setQueryParameters(String key, String... values);
 
     @Override
-    HttpRequest fragment(@Nullable String fragment);
+    default HttpRequest fragment(@Nullable String fragment) {
+        throw new UnsupportedOperationException("HttpRequest#fragment(String) is not supported by " +
+                getClass());
+    }
 
     @Override
     HttpRequest version(HttpProtocolVersion version);

servicetalk-http-api/src/main/java/io/servicetalk/http/api/StreamingHttpRequest.java

@@ -285,7 +285,10 @@ <T, S> StreamingHttpRequest transform(TrailersTransformer<T, S> trailersTransfor
     StreamingHttpRequest method(HttpRequestMethod method);
 
     @Override
-    StreamingHttpRequest fragment(@Nullable String fragment);
+    default StreamingHttpRequest fragment(@Nullable String fragment) {
+        throw new UnsupportedOperationException("StreamingHttpRequest#fragment(String) is not supported by " +
+                getClass());
+    }
 
     @Deprecated
     @Override