Upgrade Flow to the latest version

[mourner]

The Flow version we currently use for type checking is nearly 3 years old and critically outdated.

• It's extremely slow. Running flow check after changing one line of code takes 1+ min, which is unacceptable for iterative development.
• It's buggy. There have been hundreds of bugfixes since.
• It's not sound. Many typing errors are silently ignored.
• The errors are often unhelpful.

The latest version (v0.170) has radically better architecture that allows it to be orders of magnitude faster, while fixing numerous soundness and stability issues. Upgrading to it would allow us to iterate on GL JS much faster, especially when doing bigger refactoring projects. Additionally, if we commit to switching to TypeScript in the future, having better type coverage will make it much easier.

But it's not easy — simply updating the version produces several thousand type errors, some due to increased strictness and soundness, and some due to typing mistakes being silently ignored in the current version (with #11400 as an example of this).

Here's my plan for a gradual upgrade:

• Type matrix and vector calculations properly — it's a major source of errors in the newer versions. Type matrix and vector calculations #11400
• Upgrade to v0.130, redoing Upgrade Flow #9188 — now many properties that can be deleted need to be properly typed as optional, a common mistake throughout our codebase. Upgrade Flow to v0.130 #11431
• Upgrade to v0.131 that enables unsafe-addition for safer arithmetic code. Upgrade Flow to v0.131.0 #11436
• Upgrade to v0.132 that now forbids implicitly using any types, producing a ton of errors on code which is currently typed incorrectly but silently ignored. Upgrade Flow to v0.142.0 #11456
• Upgrade to v0.142 with type_first mode disabled, the latest version where you can do that. Upgrade Flow to v0.142.0 #11456
• Type-first sprint: gradually upgrade the codebase to support type_first=true architecture.
• Once type-first mode works, turn it on and upgrade to the latest version.

Type-first sprint

• Make a list of all JS files in src/, and assign batches of files across people participating in the sprint.
• For each file, remove the type_first=false line in .flowconfig, then run flow codemod annotate-exports --write --repeat <path> (see codemod docs)
• Make sure generated types make sense, fix if necessary.
• Discard .flowconfig changes and make sure test-flow passes.
• PR the changes for a batch of files to main.