Switch some defined(PETSC_ to PetscDefined(

Add automatic generated fortran support for setting and returning contexts

Major cleanup of the code for setting and returning application (previously called user) contexts
- PetscCtx ctx is now t

Add automatic generated fortran support for setting and returning contexts

Major cleanup of the code for setting and returning application (previously called user) contexts
- PetscCtx ctx is now the standard for passing in contexts
- PetscCtxRt ctx is the standard for passing out contexts, including context destroy routines based on PetscCtxDestroyFn

Both of these are typedef to void*

Also removed most use of user and userctx for context arguments now consistently named ctx

Improved documentation on PetscCtx and PetscCtxRt and on how to use contexts (including getting them) from Fortran

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Change use of void (*)(void) and void (**)(void) in the PETSc API to PetscVoidFn * and PetscVoidFn ** or PetscErrorCodeFn * or PetscErrorCodeFn **

Deprecate MPIU_BOOL which used to be for PETSc' enum Bool but now is just MPI_C_BOOL so no longer needs its own name