Support export controls

[kevinbarabash]

• parse export
• refactor Binding to be a struct instead of tuple
• update TypeScript AST to have Export field directly on decl nodes

TODO:

• [x] enforce exports on modules

I'm going to punt on enforcing export on declarations in namespaces for now. The main purpose of this work was to get top-level exports in place so that I could add support for export * from "...". This PR doesn't add support for that style of export yet. That'll happen in a followup PR.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 92.15247% with 35 lines in your changes missing coverage. Please review.

Project coverage is 83.96%. Comparing base (a34dcf4) to head (731d764).

Files with missing lines	Patch %	Lines
src/Escalier.Compiler/Prelude.fs	85.60%	19 Missing :warning:
src/Escalier.Codegen/Printer.fs	69.23%	4 Missing :warning:
src/Escalier.TypeChecker/Env.fs	42.85%	4 Missing :warning:
src/Escalier.TypeChecker/Helpers.fs	42.85%	4 Missing :warning:
src/Escalier.TypeChecker/Infer.fs	96.87%	2 Missing :warning:
src/Escalier.Codegen/Codegen.fs	95.45%	1 Missing :warning:
src/Escalier.Interop/Migrate.fs	95.23%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #365 +/- ## ========================================== - Coverage 84.08% 83.96% -0.12% ========================================== Files 22 22 Lines 12433 12552 +119 Branches 1757 1791 +34 ========================================== + Hits 10454 10539 +85 - Misses 1979 2013 +34 ```

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