Handle global leak detection for ternary operators

Summary:
**Background**: We would like the ability to check for global leaks that occur in ternary expressions.

**Problem**: The above case is unimplemented, and therefore will not catch global leaks that occur in its sub-expressions.

**Solution**: Call `forward_expression`/`forward_assignment_target` for those cases.

**Context**: This diff stack implements a global leak detection framework on top of Pyre. Previous diff adds functionality to check for leaks from lambdas.

Reviewed By: pradeep90

Differential Revision: D42935477

fbshipit-source-id: 9fa124e4a999415569cb0e02c0d6507b68c3cd03

Fix perf regression + broken perf tests

Reviewed By: grievejia

Differential Revision: D37461397

fbshipit-source-id: 90dca99a656ae1f1ea3ce1b6273e58b70b5cb280

Fix perf regression + broken perf tests

Reviewed By: grievejia

Differential Revision: D37461397

fbshipit-source-id: 90dca99a656ae1f1ea3ce1b6273e58b70b5cb280

More actionable message for "server already exist" error

Reviewed By: shannonzhu

Differential Revision: D26838895

fbshipit-source-id: 978e5ed739267ed3f3388961e1cbb47f9fdf8635

improve error messages when loading from saved state fails

Summary: As titled.

Reviewed By: grievejia

Differential Revision: D26836065

fbshipit-source-id: 6330a1e1701035d04e9a9bc99be5a0d2187d3473

Resolve concatenation of tuples via unpacking.

Summary:
Problem: We used to resolve `(1, *(2, 3))` as `Tuple[int, unknown]`. This was because we correctly resolved `(2, 3)` as `Tuple[int, int]` and then dropped the ball on the `Starred` expression because there is no type to express a naked unpacked tuple.

With variadic tuples, we can handle different kinds of unpacked tuples.

Reviewed By: dkgi

Differential Revision: D26821042

fbshipit-source-id: 7aad420ca4b2775e32617077a4f1d0e965efff30

added pysa vscode extension template (facebook#388)

Summary:
Cloned Pyre's existing VSCode extension code and changed README, package.json for Pysa. This sets up a template for further development of extension and completes [Step https://github.com/facebook/pyre-check/issues/1](https://github.com/MLH-Fellowship/pyre-check/issues/2) in the overall roadmap to creating a Language Server extension for Pysa.

Pull Request resolved: facebook#388

Reviewed By: arthaud

Differential Revision: D26781032

Pulled By: gbleaney

fbshipit-source-id: 67e0d954133d517ec7f8a8be60471a51cd76f9a1

update documentation for ocaml 4.10.2

Summary: We upgraded our version of ocaml but did not update the documentation. Let's fix it.

Reviewed By: grievejia

Differential Revision: D26674077

fbshipit-source-id: 96f7b30b666b1fb6520f34df7c5e9ab4c701edf5

Add pyre badge to readme (facebook#371)

Summary: Pull Request resolved: facebook#371

Reviewed By: pradeep90

Differential Revision: D25927938

Pulled By: dkgi

fbshipit-source-id: 180e970acf39bb947b6a116c631900e08a3b2fb1

support source-specific sanitizers

Summary: Does what it says on the tin. For the syntax, I chose to support parsing our existing `TaintSource[...]` syntax, as it already had support for multiple kinds of taint.

Reviewed By: arthaud

Differential Revision: D24853422

fbshipit-source-id: 857747d8246cde76501481378a6b7cf2e7072a2c