Bump typescript version to ~4.1.3

[chandlerprall]

Summary

Breaking change

Closes #5146 by upgrading our typescript dependency to match Kibana's pinned version.

• updated TS version in dependencies & peerDependencies
• gave a Promise in icon.test.txt an explicit return type
• convinced TS spreading searchProps in *EuiSelectableSitewideTemplate is okay
• tested resulting eui.d.ts in Kibana

Checklist

- [ ] Check against all themes for compatibility in both light and dark modes
- [ ] Checked in mobile
- [ ] Checked in Chrome, Safari, Edge, and Firefox
- [ ] Props have proper autodocs and playground toggles
- [ ] Added documentation
- [ ] Checked Code Sandbox works for any docs examples
- [ ] Added or updated jest tests

• Checked for breaking changes and labeled appropriately
  - [ ] Checked for accessibility including keyboard-only and screenreader modes
• A changelog entry exists and is marked appropriately

[kibanamachine]

Preview documentation changes for this PR: https://eui.elastic.co/pr_5182/

[thompsongl]

Nice! This is much cleaner than I expected 🦑