OPFS: if an op which needs a lock is called when no lock has been obtained, automatic...

OPFS: if an op which needs a lock is called when no lock has been obtained, automatically lock it at the start of the op and unlock it at the end of that op. This is an attempt to alleviate the cross-tab contention described in [forum post 58a377083cd24a|forum:58a377083cd24a] but it increases speedtest1 run time by approximately 4x. Perhaps auto-lock can be combined with the older idle-time-based auto-unlock to unlock such locks (but not those from xLock()) to improve this?

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