We create an injectable LockHandler that just calls the static
Lock.executeWithLocks function.
I'm not sure what's the correct place to put the LockHandler. I think
model/server is only appropriate for the actual datastore lock. This is a "per request" lock, so maybe request/lock?
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This is the initial step in adding the "lock implicitly released on request death" feature, but it's also useful on its own - easier to test Actions when we can use a fake lock.
To keep this CL simple, we keep using the old Lock as is in most places. We just choose a single example to convert to LockHandler to showcase it. Converting all other uses will be in a subsequent CL.
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