feat(browserstack-service): add accessibility support for Safari and Chrome for Testing

[harshit-browserstack]

Proposed changes

Extends Accessibility Automation in the BrowserStack service to support Safari and Chrome for Testing in addition to Chrome.

• On BrowserStack infrastructure: Chrome 95+, Chrome for Testing 141+, Safari 18.4+
• On non-BrowserStack infrastructure: Chrome 100+, Chrome for Testing 141+, Safari 18.4+

Changes:

• Adds SUPPORTED_BROWSERS_FOR_ACCESSIBILITY, MIN_BROWSER_VERSIONS_A11Y, and MIN_BROWSER_VERSIONS_A11Y_NON_BSTACK constants so minimum versions live in one place.
• Refactors validateCapsWithA11y and validateCapsWithNonBstackA11y to do per-browser validation (major/minor version compare for Safari, major-only for Chrome variants) with clearer warning messages.
• Wraps validateCapsWithNonBstackA11y in try/catch to avoid breaking the run when capability shapes are unexpected.
• Adds unit tests covering the new browser/version matrix.

Internal PR with approvals: harshit-browserstack#1

Types of changes

• Polish (an improvement for an existing feature)
• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update (improvements to the project's docs)
• Specification changes (updates to WebDriver command specifications)
• Internal updates (everything related to internal scripts, governance documentation and CI files)

Checklist

• I have read the CONTRIBUTING doc
• I have added tests that prove my fix is effective or that my feature works
• I have added the necessary documentation (if appropriate)
• I have added proper type definitions for new commands (if appropriate)

Backport Request

• This change is solely for v9 and doesn't need to be back-ported
• Back-ported PR at #XXXXX

Further comments

The new constants keep BrowserStack and non-BrowserStack minimum versions separate because the two environments have historically diverged (Chrome 95 vs 100). Keeping them as two tables makes future bumps explicit rather than accidental.

Reviewers: @webdriverio/project-committers

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: harshit-browserstack / name: Harshit (b7b87c3, ebbe842)
• ✅ login: Tanmay-Bstack / name: Tanmay Lokhande (02c858d, 85eb62a, 8da8af3, 90d9631, acea3a8, deb7239)

[harshit-browserstack]

Hi @christian-bromann, could you please review this when you have a moment? This adds Safari 18.4+ and Chrome for Testing 141+ support to the accessibility automation in the BrowserStack service. Internal approval from BrowserStack reviewers is linked in the description. Thanks!