allow app-custom src dependencies during compilation
allow app-custom src dependencies during compilation

This is useful for apps that may have moose-external dependencies that
they need to compile/build.  Sometimes a moose app file (e.g.
FooMaterial.C) can depend on a file generated by the build of an
external app dependency.  Without this addition - there is not way for
the app developer to tell us about this dependency - which prevents
parallel builds from working properly.

Fixes #17800.

jessecarterMOOSE/moose,bwspenc/moose,sapitts/moose,bwspenc/moose,milljm/moose,laagesen/moose,milljm/moose,dschwen/moose,nuclear-wizard/moose,bwspenc/moose,SudiptaBiswas/moose,milljm/moose,harterj/moose,nuclear-wizard/moose,bwspenc/moose,idaholab/moose,harterj/moose,SudiptaBiswas/moose,lindsayad/moose,lindsayad/moose,dschwen/moose,nuclear-wizard/moose,andrsd/moose,laagesen/moose,sapitts/moose,harterj/moose,sapitts/moose,nuclear-wizard/moose,sapitts/moose,lindsayad/moose,bwspenc/moose,jessecarterMOOSE/moose,laagesen/moose,lindsayad/moose,laagesen/moose,sapitts/moose,jessecarterMOOSE/moose,andrsd/moose,jessecarterMOOSE/moose,dschwen/moose,milljm/moose,SudiptaBiswas/moose,idaholab/moose,laagesen/moose,dschwen/moose,idaholab/moose,idaholab/moose,dschwen/moose,SudiptaBiswas/moose,milljm/moose,andrsd/moose,harterj/moose,SudiptaBiswas/moose,lindsayad/moose,jessecarterMOOSE/moose,idaholab/moose,andrsd/moose,andrsd/moose,harterj/moose