".plt" unpacking: require literal S-expression pattern

A literal S-expression is required instead of an S-expression that
is evaluated. Any ".plt" file created in the normal way will still
work.
file/gzip: remove use of `unit200'

The unit was just there to create an instantiable local definition
context. In modern Racket, a function body does the same job.
move `mzscheme' and `mzlib/unit200' from core to "compatibility-lib"

Also, move `mzlib/sandbox' to "compatibility-lib".
move `compile-file' to `compiler/compile-file'

The `mzlib/compile' module re-exports the moved function.

Also, fix `make-directory*' so that it never fails on an existing
directory. Remove `unstable/file', since it was just the same
clean-up of `make-directory*'.
remove core dependency on `mzlib/restart'
fix `syntax/boundmap', too

Related to PR 13911
look for default preferences file in the configuration directory

... instead of a "defaults" collection.
slatex: copy "slatex.sty" to the "lib" directory