Fixes #2482

And also add proj_context_errno_string()

Revise gie 'expect failure errno XXXX' strings

Gone are pj_malloc, pj_calloc, pj_dalloc and pj_dealloc. Their primary
function as API memory functions in proj_api.h is no longer there and
the other use as a workaround for old errno problems is no longer valid
either.

Replaced with malloc and free across the codebase.

Last user, apart from transform.cpp, was the SCH projection. Modify it
to use cart instead.

And move content of geocent.h and .cpp into transform.cpp directly, so
that it can be later wiped up easily.

This is mostly to have better OSSFuzz report. Currently a lot
of bug summaries are like
`proj4/standard_fuzzer: Divide-by-zero in s_inverse`

By prefixing the projection name, we will get better reports, like
`Divide-by-zero in airy_s_inverse`

This also makes it slightly easier to set a breakpoint by
function name.