Track open requests by their ID, so that specific requests can be
aborted instead of aborting all request for a given db name. This is
important because worker and windows at the same origin could be opening
databases and aborting their opening, but this should not affect other
scopes at the origin.
Testing: Existing WPT test suites.
Fixes: None, but part of https://github.com/servo/servo/issues/40983
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Signed-off-by: gterzian <2792687+gterzian@users.noreply.github.com>