Alternative implementation for reWriteBatchedInserts

[vlsi]

Describe the issue

Currently we rewrite the select to multi-values insert.
It requires multiple statements, and we use power-of-two packing to alleviate the overhead.

There is an alternative option:

insert into table(id, name, ...)
 select unnest(?), unnest(?), ...

Then we could bind the values as a set of arrays.

It might have the following improvements:

1. We would no longer require "power-of-two" logic
2. The query will be shorter
3. It might be faster
4. There will be no limit of "65535 binds"

TODO:

• Measure how select unnest(?), unnest(?) compares with values(...), (...), (...)
• Test if it would work with "on conflict", "merge" and so on
• Figure out if we could support values(DEFAULT, ...). It might be DEFAULT would require adjusting the column list in the into clause
• Figure out if we could support expressions in values like values(?+?, ?-?)

[davecramer]

This deserves some study for sure