[FIX] core: is_false has lots of false negatives over RPC

`is_false` relies on no small part on equality tests between the input
triplets and either `TRUE_LEAF` or `FALSE_LEAF`. While these are
defined as tuples, RPC domains will always be lists (as neither
XML-RPC nor JSON have tuples, and their arrays deserialize to Python
lists).

This is an issue, because tuple and list never compare equal. As a
result, while the in / not in predicates can succeed, the TRUE_LEAF /
FALSE_LEAF never will, and thus domains which contain either and might
shortcut (avoid a query entirely) will always go through the entire
process.

Fix by having domain normalization also ensure all triplets are
tuples: that's the first thing `is_false` does, it should never cause
issues and could fix / improve / shortcut other routines.

closes odoo/odoo#39590

Signed-off-by: Xavier Morel (xmo) <xmo@odoo.com>