Import basic codes of GC feature:
- Add basic GC related macros, data structures and APIs
- Change WASMType to WASMFuncType/AOTFuncType and re-org interp/aot codes
- Import GC opcodes and add empty opcode handling in loader and interpreter
- Implement type section loading to resolve func/struct/array type
- Implement is_subtype_of for func/struct/array, implement struct field offset calculation
- Add -G option for test_wamr.sh to test GC spec cases
Signed-off-by: Wenyong Huang <wenyong.huang@intel.com>
