Extract some helper methods for autogen targets.
Move autogen target creation to InitializeMocSourceFile.

The SetupAutoGenerateTarget method will soon be invoked at a later
time in a followup commit. We need to ensure that we create the
utility autogen target early.
cmAutogen: Rename method to InitializeAutogenTarget

This reflects better what it is doing.
cmQtAutogen: Gather tool arguments after creating generator targets.

One of the side-effects in cmGlobalGenerator::CreateGeneratorTargets
is that compile definitions from the makefile are appended to the
target. Compile definitions are read from the target directly for
generating the buildsystem, and generating the Autogen info too
early caused incomplete compile definitions to be used (#14535).

The compile definitions related code will be moved out of
CreateGeneratorTargets in a followup commit. However this change
also has the independent benefit that it causes the
GetLinkInterfaceDependentStringProperty method to be called in
SetupAutoGenerateTarget, after the creation of generator targets. In
CMake 4.0, the GetLinkInterfaceDependentStringProperty will move to
the cmGeneratorTarget class, and this is a necessary prerequisite to
that.
Extract FinalizeTargetCompileDefinitions from cmGeneratorTarget.

Call the method early in the generate step.
Merge topic 'fix-autogen-definitions' into next

c0ffa8e Extract FinalizeTargetCompileDefinitions from cmGeneratorTarget.
879b906 cmQtAutogen: Gather tool arguments after creating generator targets.
8d01a79 cmAutogen: Rename method to InitializeAutogenTarget
944da5d Move autogen target creation to InitializeMocSourceFile.
f47f1ec Extract some helper methods for autogen targets.