chore: manage typescript at workspace root

[bhongy]

Changes

• centralize typescript-related devDependencies to project root for version consistency
• centralize tsconfig to root and have package-specific tsconfig extends it for consistency
• make typescript config more strict especially around detecting null and undefined
• fix type errors
• typecheck test folders
• add Turbo task typecheck which runs tsc in typechecking mode
• set up Github Action to run typecheck task

Verification Checked the produced index.d.ts and index.js files and they're equivalent to the output produced on the main branch.

• core/dist/index.d.ts exact same output
• core/dist/index.js equivalent output (seems like munged variable names are swapped but it produces the same result), note "use strict" is removed
• react/dist/index.d.ts exact same output
• react/dist/index.js comparable output; expected the changes how we handle null and undefined in context.tsx and useForm.ts.

[changeset-bot[bot]]

🦋 Changeset detected

Latest commit: 9ef196788849bba44a02352553adf900acdd3c96

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 2 packages

| Name | Type | | ---------------- | ----- | | @formspree/react | Patch | | @formspree/core | Patch |

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Name	Status	Preview	Comments	Updated (UTC)
formspree-react-demo	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Jun 22, 2023 3:37am

[colevscode]

Might be worth a patch bump, if for no other reason, updates the changelog so we can track these improvements. To do that I suggest running yarn changeset and let the changeset bot do it's thing