1733 Auto Qt

[trisyoungs]

This PR started off as a quick "30 minutes left on a Friday" job, but has turned into a "waste the whole of Monday" task instead. This is a big PR, but most of it is just renaming and only the first and last commits are particularly interesting.

So to begin we were already using CMake's AUTOMOC option, but not AUTORCC or AUTOUIC, and were kind of half-blending the automated integration with the qt6_wrap_* mechanism (not recommended). Switching out to full auto cleans up a lot of our filenames, removing the "custom" *.hui and *Funcs.cpp namings in favour of plain old *.h and *.cpp (the latter was a legacy introduced many years ago when I was getting clashes between Qt-generated *.cpp files, from processing ui files, with my own).

However, moving to full auto introduces a problem whereby now autogenerated files are stored in many separate locations, rather than in a single build dir), meaning CMakeLists.txt have had to be adjusted in a few places in order to find the necessary ui_* files. This was a particular issue for the moduleWidgetProducer target which needed to find N ui_* files for N modules in N different locations. A solution is in place, but perhaps someone with a better relationship with CMake can implement a better one (see final commit).

Closes #1733.

[trisyoungs]

@RobBuchananCompPhys are you OK with me merging this in now, since it will cause a conflict with your other charges PR #1787, or would you like me to wait?