Centralize, rather than keeping adding constructors from any
array-like container.
A more robust implementation, likely following the converting
constructor for std::span ([span.cons]), is out of scope for C++17
and will require C++20's ranges and concepts.
[ChangeLog][QtCore][QStringView] QStringView can now be constructed
from any contiguous container, as long as they hold string-like data.
For instance, it's now possible to create a QStringView object
from a std::vector<char16_t>, a QVarLengthArray<ushort> and so on.
Change-Id: I7043eb194f617e98bd1f8af1237777a93a6c5e75
Reviewed-by: Marc Mutz <marc.mutz@kdab.com>
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