Usecase:
- Product A 10 units in stock
- Do a planned transfer of 7 units to customer
- Reserve
- Do an rpc or execute code to call copy on the stock.move.line

It will result with 2 sml that have 14 units reserve and 7 units
reserved on stock.quant

It's the same result if you create twice the stock.move.line without
updating the stock.quant at the same time. However in stable we
try to only use _update_reserved_quantity on stock.move or some
override in create/write method for 'done' stock.move.line in unlock
cases.

So we never use the copy in stable and define the basic behavior as
'we don't copy the reservation' could prevent some usecase where
the update on the stock.quant is forgotten after.

closes odoo/odoo#73870

Signed-off-by: Arnold Moyaux <amoyaux@users.noreply.github.com>