Add types to fix autocomplete.

[howmanysmall]

Add types to Roact to allow autocomplete to work. Without it, you have to either make a vague shorthand like local e = Roact.createElement or type out Roact.createElement every time you want to use it. This fixes this problem.

Checklist before submitting:

• [X] Added entry to CHANGELOG.md
• [X] Added/updated relevant tests
• [X] Added/updated documentation

[coveralls]

Coverage increased (+0.004%) to 94.86% when pulling 30ddc86c87da9badf42e85396dc49bd8808d48b8 on howmanysmall:master into 82b805a3ece0beb7b5a8628410ae8e0b1e2c282e on Roblox:master.

[github-actions[bot]]

CLA Signature Action: All authors have signed the CLA. You may need to manually re-run the blocking PR check if it doesn't pass in a few minutes.