Fix run_a11y_check.sh to use accesslint cli instead of mocking up the GH action

[jen-reeve]

Currently run_a11y_check.sh (and the associated VSC task) basically do a mockup of the GitHub Action using AccessLint/audit. But really this should just use the core or cli options from AccessLint.

Ideally would also take the extra details available (locations etc) currently in the .json/.sarif reports and include them in the .md report

[jen-reeve]

Also make it check in both light and dark mode (should add this to Github Action too if possible)