v0.50.0

Likely to cause new Flow errors:

• Fixed a bug that suppressed unrelated errors when a missing annotation error was also suppressed.

New Features:

• Added $Values type.

Notable bug fixes:

• Fixed lints appearing in Try Flow.
• Miscellaneous libdef improvements.
• Fixed a couple bugs that could lead to missing push diagnostics when using the persistent connection.
• Made $ReadOnlyArray covariant in variance checking.