[FIX] web: Find key in stringified JSON

Steps to reproduce the bug:
- In Projects, switch to the calendar view
- Click a task

Bug:
Traceback here: https://github.com/odoo/odoo/blob/7ba47e7215df69b6556a848532e4f33ef4243e83/addons/web/static/src/js/fields/basic_fields.js#L2181



TypeError: Cannot use 'in' operator to search for 'invisible' in {}

Explanation:
We could change the inherited model of CalendarView from AbstractView to BasicView but it would be adding 400 lines of code to every calendar view. So, for now, and to keep it simple, we just parse the modifiers where it's needed to.

opw:2352436
opw:2352890
opw:2354039

closes odoo/odoo#59717

Signed-off-by: backspac <backspac@users.noreply.github.com>