hdf5_ep

Reduce casts of HDcalloc()/HDmalloc() that -Wc++-compat required.

Reduce gratuitous casts---e.g., (size_t)1.

Use the right format string for a pointer.

In the H5C sanity checks, change a "size increase" variable from ssize_t
(too narrow) to int64_t (wide enough).

Parenthesize every appearance of `storage` in the macro
`H5D_CHUNK_STORAGE_INDEX_CHK(storage)` so that you can pass in an
expression like &sc and it works properly.

Disallow re-assignment of the `dset` parameter to H5D__chunk_init()
because it helped assure me that it's safe to replace the repeating
expression `&dset->shared->layout.storage.u.chunk` with `sc` throughout.

Replace lengthy expressions such as
`&dset->shared->layout.storage.u.chunk` with `sc` throughout several
functions in H5Dchunk.c ISTR that the compiler warned that `sc` was
declared but unused in a couple of functions, and then I found that `sc`
could be used in many places.  Maybe the disused `sc` appeared because a
bunch of code was copied and pasted, I don't know.  Anyway, it's a lot
tighter code now that I use `sc`.

In H5D__chunk_update_old_edge_chunks() and H5D__chunk_delete()
I actually expand `sc` and another temporary variable, `pline`,
because they're used only in !defined(NDEBUG) code.  This squashes
unused-variable warnings in the defined(NDEBUG) configuration.

Don't drop the `volatile` qualification with a cast in
tools/src/h5import/h5import.c.