idl_parser.cpp ignores $schema in input json (#4382)
idl_parser.cpp ignores $schema in input json (#4382)

* idl_parser.cpp ignores $schema in input json
#4381

* idl_parser.cpp: Fixed ci error signed unsigned comparison

* idl_parser.cpp: replaced case insensitive search for $schema with case sensitive search

* idl_parser.cpp: Expecting a string constant after $schema
#4382

rw/flatbuffers,google/flatbuffers,alexames/flatbuffers,evolutional/flatbuffers,hgl888/flatbuffers,royalharsh/flatbuffers,rw/flatbuffers,chenkai036/flatbuffers,chenkai036/flatbuffers,stewartmiles/flatbuffers,evolutional/flatbuffers,endorph-soft/flatbuffers,google/flatbuffers,royalharsh/flatbuffers,pjulien/flatbuffers,alexames/flatbuffers,google/flatbuffers,pjulien/flatbuffers,google/flatbuffers,stewartmiles/flatbuffers,evolutional/flatbuffers,google/flatbuffers,evolutional/flatbuffers,pjulien/flatbuffers,chenkai036/flatbuffers,google/flatbuffers,rw/flatbuffers,endorph-soft/flatbuffers,DavadDi/flatbuffers,DavadDi/flatbuffers,rw/flatbuffers,endorph-soft/flatbuffers,alexames/flatbuffers,rw/flatbuffers,google/flatbuffers,DavadDi/flatbuffers,stewartmiles/flatbuffers,google/flatbuffers,DavadDi/flatbuffers,google/flatbuffers,stewartmiles/flatbuffers,pjulien/flatbuffers,evolutional/flatbuffers,google/flatbuffers,rw/flatbuffers,hgl888/flatbuffers,pjulien/flatbuffers,google/flatbuffers,rw/flatbuffers,endorph-soft/flatbuffers,DavadDi/flatbuffers,google/flatbuffers,royalharsh/flatbuffers,pjulien/flatbuffers,evolutional/flatbuffers,hgl888/flatbuffers,royalharsh/flatbuffers,chenkai036/flatbuffers,stewartmiles/flatbuffers,pjulien/flatbuffers,pjulien/flatbuffers,evolutional/flatbuffers,pjulien/flatbuffers,stewartmiles/flatbuffers,chenkai036/flatbuffers,alexames/flatbuffers,alexames/flatbuffers,pjulien/flatbuffers,royalharsh/flatbuffers,DavadDi/flatbuffers,endorph-soft/flatbuffers,stewartmiles/flatbuffers,alexames/flatbuffers,chenkai036/flatbuffers,rw/flatbuffers,hgl888/flatbuffers,endorph-soft/flatbuffers,chenkai036/flatbuffers,hgl888/flatbuffers,alexames/flatbuffers,alexames/flatbuffers,evolutional/flatbuffers,evolutional/flatbuffers,rw/flatbuffers,stewartmiles/flatbuffers,google/flatbuffers,evolutional/flatbuffers,endorph-soft/flatbuffers,royalharsh/flatbuffers,stewartmiles/flatbuffers,rw/flatbuffers,alexames/flatbuffers,royalharsh/flatbuffers,endorph-soft/flatbuffers,alexames/flatbuffers,alexames/flatbuffers,stewartmiles/flatbuffers,royalharsh/flatbuffers,alexames/flatbuffers,google/flatbuffers,alexames/flatbuffers,royalharsh/flatbuffers,pjulien/flatbuffers,endorph-soft/flatbuffers,evolutional/flatbuffers,chenkai036/flatbuffers,alexames/flatbuffers,rw/flatbuffers,hgl888/flatbuffers,evolutional/flatbuffers,alexames/flatbuffers,stewartmiles/flatbuffers,pjulien/flatbuffers,evolutional/flatbuffers,stewartmiles/flatbuffers,royalharsh/flatbuffers,rw/flatbuffers,google/flatbuffers,endorph-soft/flatbuffers,chenkai036/flatbuffers,chenkai036/flatbuffers,stewartmiles/flatbuffers