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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checkbadSource: enforce proper style in makefiles

clang-format: update to v21 (and update CI)

Convert some SETERRQ() to PetscCheck()