Reject unresolved reflected object types during deserialize

[michaelsam94]

Summary

• reject reflected object/vector/array types that do not resolve to a valid struct/table index during Type::Deserialize
• add a regression test for issue SEGV in StructDef::Deserialize via IsStruct on a bfbs schema that passes VerifySchemaBuffer #9144 where VerifySchemaBuffer passes but Parser::Deserialize previously crashed

Fixes #9144

Tests

• clang++ -std=c++17 -O0 -Iinclude -I. -x c++ - src/idl_parser.cpp src/reflection.cpp src/util.cpp -o /tmp/flatbuffers_issue_9144_test with an inline issue SEGV in StructDef::Deserialize via IsStruct on a bfbs schema that passes VerifySchemaBuffer #9144 harness, then /tmp/flatbuffers_issue_9144_test
• clang++ -std=c++17 -O0 -Iinclude -I. -c src/idl_parser.cpp -o /tmp/idl_parser.o
• clang++ -std=c++17 -O0 -Iinclude -I. -c tests/monster_test.cpp -o /tmp/monster_test.o
• git diff --check

Note: cmake, bazel, and clang-format are not installed in this local environment, so I could not run tests/TestAll.sh or project formatting here.