Name the exception ids and address review comments

Add detail::exception_id, a scoped enum with one named enumerator per
documented exception id, and use it for every id in the library. The
create() functions get an overload for it; the int overloads stay for
user code.

Following the review of #5783: add binary_reader::invalid_byte() and
length_type_error(), basic_json::throw_subscript_wrong_type(), move the
fuzzer includes and the using-declaration into fuzzer_common.hpp, and
rename test_sax.hpp to sax_event_loggers.hpp.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

tests/src/unit-deserialization.cpp

@@ -36,7 +36,7 @@ using nlohmann::json;
 #include <string>
 #include <valarray>
 
-#include "test_sax.hpp"
+#include "sax_event_loggers.hpp"
 
 using utils::SaxEventLogger;
 using utils::SaxEventLoggerExitAfterKey;