Issue #3266568 by mxr576, sourabhjain, quietone: Refactor array_merge() usage in loops as possible for performance

Issue #2883680 by dawehner, Wim Leers, tim.plunkett, larowlan: Force all route filters and route enhancers to be non-lazy

Issue #2659070 by Wim Leers, dawehner, tic2000, Crell: REST requests without Content-Type header: unhelpful response significantly hinders DX, should receive a 415 response