chore: enable query engine v2 by default

[wangrunji0408]

As the final step to introduce the new planner #703, this PR reorganizes code structures, moves the legacy binder/planner/optimizer/executor to the v1 module, and enables v2 by default. The legacy modules will be kept for a while, as a reference to improve the new one further. But it's not expected to add new features to it.

Here is a rough statistic to compare the lines of code of the two versions:

Module	v1	v2
Binder	2071	1115
Planner	4731	1411
Executor	2258*	1307
Total	9060	3833

* exclude unused executors
* use loc to count lines of code

Even taking into account the lack of test code in v2 for now, it is still much simpler than v1, using half of the code to achieve the same goal. Thanks to egg, we can make RisingLight lite again!