QtAutogen: Regenerate qrc files if their input changes (#15074)

Get dependencies from the output of ``rcc --list`` if using
Qt 5.  Otherwise process the file in the same way as the
qt4_add_resources macro.

This does not work for RCC files which are generated.

The cmake_autogen build step is implemented as a PRE_BUILD step
of the target currently if possible, rather than a standalone
custom target.  This is to keep the number of (synthesized)
custom targets that appear in the UI low, but in some cases
it is necessary to fall back to a full custom target.

Fall back to a full custom target for the VS builds if autorcc
is used.
Merge topic 'autorcc-depends' into next

6e1c359f QtAutogen: Regenerate qrc files if their input changes (#15074)