VL: add support for typedefs as blockitems

This adds at least parsing support for typedefs in functions, tasks,
and block statements (begin/end or fork/join statements).

It also extends scopestacks, so it's possible that this means that
these typedefs might actually work in a deeper way, but this hasn't
been tested yet.

Misc changes:
  - Minor reduction of dependencies for vl/mlib/writer.lisp.
  - Rename parser/parser to parser/top
  - Rename lexer/lexer to lexer/top
  - Rename preprocessor/preprocessor to preprocessor/top

books/centaur/vl/kit/pp.lisp

@@ -31,7 +31,7 @@
 (in-package "VL")
 (include-book "progutils")
 (include-book "../util/print")
-(include-book "../loader/preprocessor/preprocessor")
+(include-book "../loader/preprocessor/top")
 (include-book "centaur/getopt/top" :dir :system)
 (include-book "centaur/misc/memory-mgmt" :dir :system)
 (include-book "std/io/read-file-characters" :dir :system)

books/centaur/vl/loader/lexer/tests.lisp

@@ -29,7 +29,7 @@
 ; Original author: Jared Davis <jared@centtech.com>
 
 (in-package "VL")
-(include-book "lexer")
+(include-book "top")
 (local (include-book "../../util/arithmetic"))
 
 (program)