[FIX] web: typo calendar highlight -> ok now

Adapt calendar highlight option (that "highlight" event linked to the
record we come from) to current JS framework data structures.

note: this changeset also fixes the original `_compute_is_highlighted`
that was would trigger CacheMiss errors, and also adds back the CSS for
highlighting that was lost between 12.0 and 13.0 version.

opw-2131494
closes #40791

closes odoo/odoo#41077

X-original-commit: da56e3e7
Signed-off-by: Nicolas Lempereur (nle) <nle@odoo.com>