Update references in the manual pages to use Sphinx citation processing

Merge branch 'barry/2023-11-28/doc-petsccall-vs-petscassert/release' into 'release'

Clarify in the manual pages the use of PetscCheck() vs PetscAssert()

See merge request petsc/petsc!7066

Clarify in the manual pages the use of PetscCheck() vs PetscAssert()

Add more details to developers documentation on how to add references to manual pages

Spell matlab correctly as MATLAB

Commit-type: housekeeping

doc: fix sowing, c2html URLs

Document new header-guard style

Fixes for bibtex processing

Commit-type: housekeeping

add to developers documentation how to add references to manual pages with cite

Testing: Add 'temporaries:' field to the test suite

It's nice when the output that needs to be tested goes to stdout, and we
can do that with our own viewers, but some output that needs to be
tested

Testing: Add 'temporaries:' field to the test suite

It's nice when the output that needs to be tested goes to stdout, and we
can do that with our own viewers, but some output that needs to be
tested can only be written to temporary files. An example is MPE
logging, which produces a .clog2 file, let's say it's called ex30.clog2.

We can access that file through the test suite:

/*TEST

test:
filter: strings ex30.clog2 | grep "Petsc"

TEST*/

But the problem is that ex30.clog2 will stay in the test build
directory. Suppose the test breaks and the program does not write
the ex30.clog2 file: then a stale version of that file will be read.

This change allows us to write the test as:

/*TEST

test:
temporaries: ex30.clog2
filter: strings ex30.clog2 | grep "Petsc"

TEST*/

which indices that (the localized version of) `rm -f ex30.clog2` will
run before the test.

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Rename PetscValidPointer -> PetscAssertPointer