cmGlobalGenerator: Refactor member cleanup between configures

Factor member cleanup out from cmGlobalGenerator::Configure and the
destructor into a dedicated helper to avoid duplication.  This fixes
clearing of BuildExportSets between configures.
cmAutogen: Extract some helper methods for autogen targets.

These snippets will soon be needed from multiple methods.
cmAutogen: 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.
cmAutogen: Gather tool arguments after creating generator targets.

This change causes the GetLinkInterfaceDependentStringProperty method,
called in SetupAutoGenerateTarget, after the creation of generator
targets. In CMake 4.0, the GetLinkInterfaceDependentStringProperty
will move to the cmGeneratorTarget class, and this patch is a necessary
prerequisite to that.
Merge topic 'clear-generator-data'

5cf1120 cmGlobalGenerator: Refactor member cleanup between configures
Merge topic 'refactor-autogen-setup'

944277d cmAutogen: Gather tool arguments after creating generator targets.
d2f4b1e cmAutogen: Rename method to InitializeAutogenTarget
45735f3 cmAutogen: Move autogen target creation to InitializeMocSourceFile.
20a234d cmAutogen: Extract some helper methods for autogen targets.