This change saves a small amount of space in cross-reference files
and some space in loaded cross-reference information.
It also saves work converting strings to mutable on deserialize,
although the performance difference seems negligible.
Related to the already fixed PR 12114 and PR 12133, which motivated the
error, and a few additional typos of the same kind.
(Note that it uses the symbols, but that's how they'll render anyway.)
For example, if you make a multi-column table with a
`racketblock' in each column, then the columns size
to fit the code --- instead of forcing the table width
to match the page width and forcing each column to take
an equal share width.
For HTML, the style used in the output of `racketblock' now
disables line wrapping, and the Rkt text styles inherit
line-wrap behavior. This doesn't solve the general problem
of code overflowing the horizontal space, but it makes the
failure mode usefully better.
A new 'vertical-inset nested-flow style is used by
`defproc', `defform', etc. It has no effect for HTML,
but it introduces suitable vertical space for Latex output
(in case you want to use `defproc' in a SIGPLAN-format
paper, for example).
