feat: emit an event when accessing restricted path in File System Access API (#43162)

* fix: show a dialog when accessing restricted path in File System Access API

Co-authored-by: Shelley Vohr <shelley.vohr@gmail.com>

* fix: allow overriding initial blocked paths

Co-authored-by: Shelley Vohr <shelley.vohr@gmail.com>

* docs: fix doc

Co-authored-by: Shelley Vohr <shelley.vohr@gmail.com>

* Update docs/api/session.md

Co-authored-by: Erick Zhao <erick@hotmail.ca>

Co-authored-by: Shelley Vohr <shelley.vohr@gmail.com>

* fix: change block to deny for consistency

Co-authored-by: Shelley Vohr <shelley.vohr@gmail.com>

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Co-authored-by: trop[bot] <37223003+trop[bot]@users.noreply.github.com>
Co-authored-by: Shelley Vohr <shelley.vohr@gmail.com>