Add type definitions for StyleOptions

[corinagum]

Fixes #2100

Changelog Entry

• Resolves #2100. Add types declarations for Style Options in api bundle, by @corinagum, in PR #3818

Description

By popular request! This set of changes provides type declarations for Web Chat's style options.

Design

Types file is exported to /types under api package.

Specific Changes

• Clean up of StyleOption props
  • Several props were spread across two defaultStyleOptions.js :o
  • Update several props from null / empty string default value to undefined
  • Alphabetize props by category
• Delete defaultStyleOptions.js in /component/Styles/ package
• Add typescript linting to eslint

• I have added tests and executed them locally
• I have updated CHANGELOG.md
• I have updated documentation

Review Checklist

This section is for contributors to review your work.

• Accessibility reviewed (tab order, content readability, alt text, color contrast)
• Browser and platform compatibilities reviewed
• CSS styles reviewed (minimal rules, no z-index)
• Documents reviewed (docs, samples, live demo)
• Internationalization reviewed (strings, unit formatting)
• package.json and package-lock.json reviewed
• Security reviewed (no data URIs, check for nonce leak)
• Tests reviewed (coverage, legitimacy)

[compulim]

Minor changes.