Each typed module now defines a submodule named `type-decl`.
This module performs the type environment initialization (along
with other environment updates) when invoked. Additionall,
every typed module, when invoked, performs a for-syntax addition
to a list specifying the submodules that need invocation.
This invocation is then performed by the `#%module-begin` from
Typed Racket.
The `type-decl` module always goes at the beginning of the
expanded module, so that it's available at syntax-time for all
the other submodules. This involved adding pre- and post-
syntaxes for the results of typechecking.
This allows significant runtime dependency reduction from the
main `typed/racket` and `typed/racket/base` languages (not yet
complete).
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