Q_DECLARE_METATYPE: Do not re-register types

When Q_DECLARE_METATYPE is used, we often end up re-registering types as
typedefs of themselves. This is because with Q_DECLARE_METATYPE, we set
a legacy register operation which calls (after some indirection)
QMetaType::registerNormalizedType.
We still need to support this to preserve compatibility in the presence
of typedefs and namespaced types. However, there is no reason to do the
wasteful work of normalizing the typename at runtime and adding memory
overhead to have a type registered as a typedef of itself.

We can skip the type normalization work by checking whether the name in
the metatype interface equals that of the typename. We still need to
make sure that the converter and view functions are registered, though.

Moreover, we can fix the check in qRegisterNormalizedMetaType to only
call registerNormalizedTypedef if the new name doesn't match the name
stored in the metatype.

Fixes: QTBUG-93841
Change-Id: Icfe42c349b23add630fe3c761362b60e9e9aaa2b
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Andrei Golubev <andrei.golubev@qt.io>
Reviewed-by: Lars Knoll <lars.knoll@qt.io>

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