Add QChronoTimer, a timer with nanoseconds precision

The interval in QTimer is a QProperty of type int, which means it's
limited to the number of milliseconds that would fit in an int (~24
days), this could cause overflow if a user constructs a QTimer with an
interval > INT_MAX milliseconds. And it can't be easily changed to use
qint64/std::chrono::nanoseconds:
  - changing the getters to return qint64 means user code would have
    narrowing conversions
  - the bindable QProperty interval can't be changed to qint64 during
    Qt6's lifetime without the risk of breaking user code
  - adding a new bindable QProperty that is qint64/nanoseconds is an
    option, but it has the complication of what to do with the int
    interval; set it when setInterval(milliseconds) is used by using
    saturation arithmetic? and what about notifying observers of the
    changed interval?

Thus the idea of creating a new stop-gap class, QChronoTimer, as a
cleaner solution. Both classes use QTimerPrivate.

During the lifetime of Qt6, QTimer's interval range is about 24 days,
whereas QChronoTimer's interval range is about 292 years
(duration_cast<years>nanoseconds::max()).

Currently the plan is to fold QChronotTimer back into QTimer in Qt7.

Mark all QPropertyS in the new class as FINAL since they aren't
intended to be overridden; this offers a performance boost for QML[1].

[1] https://lists.qt-project.org/pipermail/development/2024-February/044977.html

[ChangeLog][QtCore] Added QChronoTimer, which uses a
std::chrono::nanoseconds intervals, as a replacement for QTimer.

Fixes: QTBUG-113544
Change-Id: I71697f4a8b35452c6b5604b1322ee7f0b4453f04
Reviewed-by: Thiago Macieira <[email protected]>
Reviewed-by: Qt CI Bot <[email protected]>

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