[IMP] core: simplify get_domain_identifier
[IMP] core: simplify get_domain_identifier

* we can just get the variable names once for the entire expression,
  no need to bother doing it bit by bit
* avoid blowing up when the domain contains computations *around*
  segments.

closes odoo/odoo#40642

Signed-off-by: Raphael Collet (rco) <fcee45b878db1f337818c5c606c1542797080a40@openerp.com>

ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo