Use a shorter license for FindWix.cmake.
Don't try to detect WiX 4.0.

It's likely to have major differences that would need changes
elsewhere anyway.
Clarify comment about the registry key search.
Misc changes in FindWix.cmake.

Swapped the arguments of _WIX_COMPILE to get the output variable first
(for consistency with many things in CMake), added an underscore to vars
from CMAKE_PARSE_ARGUMENTS, etc.
Make the dir for Qt libraries configurable independently.

Instead of putting the Qt DLLs in PFSubdir, I put them in QtDir,
which this main.wxs happens to set to the same as PFSubdir,
but isn't necessarily that way.
Installer: remove File/@Name attributes.

File/@Name attributes are redundant, since they default to the filename
of the path specified in File/@Source.
Installer: remove Component/@Id attributes.

If @Id is missing, it gets auto-generated from the name of the File
specified as KeyPath, and those names are good enough.
Add components for QtNetwork, QtQuick, QtQml.