[FIX] project: improve tags name_search robustness

Description:
The commit 05855b6b introduced a
fast-path for the name_search on tags from the form view of tasks.
But the implementation was too complex and wasn't handling correctly
all possible operators (it just had a fallback on the default
parent name_search implementation).
The aim is to simplify the code for better robustness and
maintainability long term.

Fix:
Convert the query to it's equivalent python code. It has a slight
performance regression than the previous implementation (we are
making 3 queries worse-case instead of 1), but the regression is
non-significant and not critical.

Affected versions:
16.0 up to master

Reference:
task-3503721

closes odoo/odoo#135323

Signed-off-by: Audric Onockx (auon) <auon@odoo.com>