Extract citationSuffix, citationPrefix.cite-prefix

In transforming pandoc Cite to citeproc Citation,
extract a `citationSuffix` and `citationPrefix` from the
last item's suffix and first item's prefix, respectively, if
they contain a `|` character which separates the item's suffix
or prefix from the whole Citation's.

for example:

    [for example, see |@C1; @A3; @B4|, and others]

Here "for example, see" acts as a prefix for the whole
group and will remain at the beginning even if the citation
items are reordered by citeproc. Similarly, ", and others"
will be a suffix for the whole group.

Closes #10894.

Notes:

1. The org reader now adds global prefixes and suffixes the
same way as the Markdown reader: as affixes to the first item's
prefix or the last item's suffix, separated by a pipe (`|`).

2. The org writer, however, has not been modified to convert the
`|` to a `;`, as required by org-cite syntax.

3. This change doesn't currently do what one would expect, because
of changes that were made to citeproc to prevent citation items
with prefixes and suffixes from being sorted.  Hence in
`test/command/10894.md`, we have test output
```
(Doe, 2020; Smith, 2021)
```
without affixes, but
```
(see Smith, 2021; Doe, 2020, and others)
```
with affixes.  To make this work well, we'd need to remove the citeproc
code that prevented bad results before we had proper global
prefixes and suffixes.  However, removing this code would mean that
existing documents would render differently, unless the new pipe
syntax for citation affixes were used.  That may be something we want
to avoid.

4. The use of pipes to separate out global affixes from item-level
affixes is a kludge that could be avoided if we added additional
fields to Cite in the pandoc AST. However, AST changes are disruptive,
so perhaps it's not worth doing that.

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