[FIX] web: current date

- Set the OS in a timezone such as the current day is different from the
  day in UTC (e.g. America/Nome before 10:00 AM or Australia/Melbourne
  after 3:00 PM)
- Open any datepicker
- The 'little triangle' indicating the current day is wrongly set (one
  day before or after)

Knowing that Odoo always creates momentjs date and datetime with the
`UTC` flag set to `true`, the `bootstrap-datetimepicker` does something
which seems inconsistent.

First, it retrieves the `viewDate`, and sets it to the beginning of the
month and week in:

https://github.com/odoo/odoo/blob/1c6c504215f3ef09e6336c92c9d350e87599eaa1/addons/web/static/lib/bootstrap-datetimepicker/src/js/bootstrap-datetimepicker.js#L725

In this part, it is important to note that each `startOf` functions
called sets the hours/minutes/seconds to zero. It means that the
reference time is changed.

Then, it iterates on this newly created date, and determines `today` by
comparing it to `getMoment()` in:

https://github.com/odoo/odoo/blob/1c6c504215f3ef09e6336c92c9d350e87599eaa1/addons/web/static/lib/bootstrap-datetimepicker/src/js/bootstrap-datetimepicker.js#L748

However, `getMoment()` returns the current date and time, but with the
`UTC` flag set to `false`.

Therefore, we compare a UTC datetime on which the reference time has
been changed to a non-UTC datetime, which fails to give the appropriate
current day.

There are two approaches to solve this. The first possibility is to
change the way Odoo defines momentjs dates and datetimes, maybe by
removing the `UTC` flag at creation. This sounds like a bad idea, since
other widgets or views (such as the calendar or the pivot view) make use
of them. This is likely to introduce a bunch of new issues with TZ in
these views. The second approach is patching the library to fit our use.
Although we usually don't do such a thing, this allows to specifically
solve this use case, and in particular placing the 'small triangle' at
the appropriate date without impacting any other part of the system or
the library. It can be easily performed by comparing the dates and the
months to make it work.

opw-1915251

closes odoo/odoo#30538

addons/web/static/lib/bootstrap-datetimepicker/src/js/bootstrap-datetimepicker.js

@@ -723,6 +723,9 @@
                 }
 
                 currentDate = viewDate.clone().startOf('M').startOf('w').startOf('d');
+                // !! ODOO FIX START !!
+                var now = getMoment();
+                // !! ODOO FIX END !!
 
                 for (i = 0; i < 42; i++) { //always display 42 days (should show 6 weeks)
                     if (currentDate.weekday() === 0) {
@@ -745,7 +748,9 @@
                     if (!isValid(currentDate, 'd')) {
                         clsNames.push('disabled');
                     }
-                    if (currentDate.isSame(getMoment(), 'd')) {
+                    // !! ODOO FIX START !!
+                    if (currentDate.date() === now.date() && currentDate.month() === now.month() && currentDate.year() === now.year()) {
+                    // !! ODOO FIX END !!
                         clsNames.push('today');
                     }
                     if (currentDate.day() === 0 || currentDate.day() === 6) {