Introduce shared UI folder

[teenoh]

🌟 What is the purpose of this PR?

This is a follow up to #453. It introduces the new shared/ui folder which includes primitive components that are used in the frontend codebase. It also introduces shared/icons for our icons.

⚠️ Known issues

🐾 Next steps

• create shared/layout for page layout components

🔍 What does this change?

• Adds a new shared/ui folder which contains UI primitives and theme
• Updates codebase to pull primitives/theme from shared/ui
• Adds a shared/icons folder for our icons

📜 Does this require a change to the docs?

• No

🔗 Related links

• Asana task (internal)

🛡 What tests cover this?

• None

❓ How to test this?

1. There are no visual changes, the app should still work without breaking

📹 Demo

---

• To see the specific tasks where the Asana app for GitHub is being used, see below:
  • https://app.asana.com/0/0/1202059478682673

[semgrep-app]

Semgrep found 1 react-props-injection finding:

• packages/hash/frontend/src/shared/ui/button.tsx: L89-107

Inject arbitrary props into the new element. It may introduce an XSS vulnerability.

_{⚪️ This finding does not block your pull request.
🙈 From typescript.react.security.audit.react-props-injection.react-props-injection.}

[kachkaev]

Thank you @teenoh! The diff makes sense!