MuonEventTPCnv: Fix genconf warnings.

TPCnv libraries declare Gaudi plugin factories for the TP converters.
Normally, the TPCnv libraries should not be linked against libraries
other than the EventPool libraries.  However, it is possible for one
TPCnv library to link against another TPCnv library.
In that case, genconf may emit warnings that one library's factory
is visible from another.  Clean up by moving TPCnv factories into their
own libraries (linked against the corresponding TPCnv library).

MuonSpectrometer/MuonCnv/MuonEventTPCnv/CMakeLists.txt

-# Copyright (C) 2002-2022 CERN for the benefit of the ATLAS collaboration
+# Copyright (C) 2002-2024 CERN for the benefit of the ATLAS collaboration
 
 # $Id: CMakeLists.txt 730483 2016-03-16 16:03:14Z harkusha $
 ################################################################################
@@ -11,7 +11,7 @@ atlas_subdir( MuonEventTPCnv )
 find_package( GeoModel COMPONENTS GeoModelKernel )
 
 # Component(s) in the package:
-atlas_add_tpcnv_library( MuonEventTPCnv
+atlas_add_library( MuonEventTPCnv
    MuonEventTPCnv/*.h src/*.cxx
    src/MuonRIO_OnTrack/*.cxx
    MuonEventTPCnv/MuonCompetingRIOsOnTrack/*.h
@@ -31,6 +31,11 @@ atlas_add_tpcnv_library( MuonEventTPCnv
    EventPrimitives MuonReadoutGeometry MuonIdHelpersLib TrkEventPrimitives
    TrkMeasurementBase )
 
+atlas_add_tpcnv_library( MuonEventTPCnvFactories
+   src/factories/*.cxx
+   PUBLIC_HEADERS MuonEventTPCnv
+   LINK_LIBRARIES MuonEventTPCnv )
+
 atlas_add_dictionary( MuonEventTPCnvDict
    MuonEventTPCnv/MuonEventTPCnvDict.h MuonEventTPCnv/selection.xml
    LINK_LIBRARIES MuonEventTPCnv )