Restructure HTML tests

[compulim]

Changelog Entry

(No changelog for test infrastructure changes.)

Description

Streamlining DX for writing tests.

Design

• Snapshot located side-by-side with test files
  • Diff snapshot also located side-by-side
• No need to write .js entrypoint file
  • Also lacking the ability to have a single .js running .html multiple times with different arguments, need to think how to make this better
• Separating jest.config.js as html and html2 tests has conflicting changes
  • Mainly, html2 requires test environment to be set inside jest.config.js due to limitation on Jest side

Specific Changes

• Added new Jest test transformer for "html2" tests for "entrypoint-less" tests
• Added new argument host.snapshot('local') to place the snapshot side-by-side to the test file
• Moved preChat* tests to "html2"

• 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)

[OEvgeny]

This looks cool!