feat: EAA 2025 - high contrast UI and voice guidance changes

[alkalinecoffee]

Adds a new Accessibility.highContrastUI method to the spec, returning a boolean denoting whether the user has selected to have high contrast UI mode enabled. This method will be available in the core SDK.

This PR also adds a new navigationHints property to the Accessibility.voiceGuidanceSettings response denoting whether or not the user has opted to have additional navigation hints synthesized.

Both of these changes are to conform to requirements of the European Accessibility Act.

A new Accessibility specification doc has also been added to capture not only the above changes but also capture existing accessibility module functionality.

[github-actions]

MFOS standalone sanity report - CORE,MANAGE,DISCOVERY:
Total Passes - 499 Failures - 0 Pending - 0 Skipped - 28
Report JSON/HTML Files: https://github.com/rdkcentral/firebolt-apis/suites/30951060761/artifacts/2194828580
Job Logs: https://github.com/rdkcentral/firebolt-apis/actions/runs/11862573544

[github-actions]

Failed to create a report:
Job logs: https://github.com/rdkcentral/firebolt-apis/actions/runs/12677230315

[github-actions]

Failed to create a report:
Job logs: https://github.com/rdkcentral/firebolt-apis/actions/runs/12696601496

[github-actions]

Failed to create a report:
Job logs: https://github.com/rdkcentral/firebolt-apis/actions/runs/12696655480

[github-actions]

Failed to create a report:
Job logs: https://github.com/rdkcentral/firebolt-apis/actions/runs/12696878738

[github-actions]

Failed to create a report:
Job logs: https://github.com/rdkcentral/firebolt-apis/actions/runs/12895609893

[github-actions]

Failed to create a report:
Job logs: https://github.com/rdkcentral/firebolt-apis/actions/runs/12936114957