[FIX] web: don't apply tz on daterangepicker input field

Issue:
When opening the daterangepicker, but not modifying anything and
closing it, and then discarding the record, the timezone is
reapplied on the input. (value in DB is correct).

Steps to reproduce:
- Install an app that has a daterange field (ex: FSM in 14, Project
  for 15->saas-15.2)
- Edit the daterange, don't change anything, close it, discard the
  record.
- Observe the timezone has been reapplied on the input value.

Cause:
When opening the daterangepicker, the initial dates read from the
input field were already localized based on the tz, but the
daterangepicker object expect it to receive datetime in utc.

Fix:
Parse the input and make sure it's in utc.

Affected versions:
- 14.0
- 15.0
- saas-15.2

opw-3342274

closes odoo/odoo#127962

Signed-off-by: Bruno Boi (boi) <boi@odoo.com>