fix: fix the context management for aggregate functions and release the memory used for the global js context

- Add reference counting to globaljs_context to ensure proper cleanup
  order
- Prevent JS_FreeRuntime assert failure by ensuring all JSValues are freed
   first
- Reset the aggregate context for each invocation of a window functions using sqlite3_aggregate_context. With this fix the xFinal callback is now called as expected.

Author: andinux