Add an option to the opfs-sahpool VFS which tells it to ignore a previous init failur...

Add an option to the opfs-sahpool VFS which tells it to ignore a previous init failure and retry, as an opt-in workaround for a browser quirk which occasionally denies OPFS access on the first attempt and permits it on subsequent attempts. This resolves [https://github.com/sqlite/sqlite-wasm/issues/79|issue #79 of the npm distribution].

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