Support GenericFunction.name passed as a quoted_name

Support GenericFunction.name passed as a quoted_name

A function created using :class:`.GenericFunction` can now specify that the
name of the function should be rendered with or without quotes by assigning
the :class:`.quoted_name` construct to the .name element of the object.
Prior to 1.3.4, quoting was never applied to function names, and some
quoting was introduced in :ticket:`4467` but no means to force quoting for
a mixed case name was available.  Additionally, the :class:`.quoted_name`
construct when used as the name will properly register its lowercase name
in the function registry so that the name continues to be available via the
``func.`` registry.

Fixes: #5079
Change-Id: I0653ab8b16e75e628ce82dbbc3d0f77f8336c407