ConvertToCFG: properly remap nested function attributes.

Array attributes can nested and function attributes can appear anywhere at that
level.  They should be remapped to point to the generated CFGFunction after
ML-to-CFG conversion, similarly to plain function attributes.  Extract the
nested attribute remapping functionality from the Parser to Utils.  Extract out
the remapping function for individual Functions from the module remapping
function.  Use these new functions in the ML-to-CFG conversion pass and in the
parser.

PiperOrigin-RevId: 221510997