Cleanup get_json_object

[ttnghia]

This does some cleaning up work, including:

• Change enum type to inherit from int8_t and reorganize class member variables to reduce padding. As such, class instances occupy less memory.
• Add const and static qualifier to member functions.
• Remove redundant code.
• Construct path commands without stream sync, etc.

No new functionality is added in this PR.

[ttnghia]

build