Instead of overloads and generic string literals with runtime checks,
use a dedicated Tag type for specifying the font feature. The Tag type
can only be instantiated with a string literal of exactly 4 characters
(plus the terminating null)l; longer or shorter literals result in a
compile time error.
Constructing a Tag from any other string type is possible through the
named fromString constructor, in which case we can only check the length
and warn at runtime.
The type's API is almost completely constexpr so that we can use it to
calculate e.g. enum values.
Task-number: QTBUG-117046
Change-Id: I31038c7c6fd2b843a105b032f021e506b0b60822
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@qt.io>
bde443801f