Fix the inconsistent usage of #if [!]defined XXX compared to defined(XXX)

Thanks-to: Pierre Jolivet

An LLM Claude detected the incosnsitency it was not used to remove the inconsistency

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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use standard bool instead of enum

PetscBool is equivalent to _Bool/bool in C

For C standards prior to C23, true = 1 and false = 0 are defined in <stdbool.h>.
For C23, true and false are real keywor

use standard bool instead of enum

PetscBool is equivalent to _Bool/bool in C

For C standards prior to C23, true = 1 and false = 0 are defined in <stdbool.h>.
For C23, true and false are real keywords.

The Fortran equivalent is logical(C_BOOL) with C_BOOL from
ISO_C_binding.

The C and the C++ standard do not specify the size of Booleans, but they
typically have a size of 1 Byte with b00000000 for false and b00000001 for true.
When using compilers from the same vendor, it is sane to assume that
_Bool/bool in C and bool in C++ are fully compatible. But that is not
guaranteed by the standards

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