AK: Rename TestMemoryStream.cpp to TestStream.cpp.

Author: https://github.com/asynts
Commit: https://github.com/SerenityOS/serenity/commit/31e7f435cb5
Pull-request: https://github.com/SerenityOS/serenity/pull/3220
Reviewed-by: https://github.com/awesomekling

AK/Tests/TestStream.cpp

@@ -108,4 +108,4 @@ TEST_CASE(seeking_slicing_offset)
     EXPECT(compare({ expected2, sizeof(expected2) }, { actual2, sizeof(actual2) }));
 }
 
-TEST_MAIN(MemoryStream)
+TEST_MAIN(Stream)