Previously, calling the bake operator was always creating a job that will
be run in parallel to Blender. This is good when baking from the UI, but may
be undesired when baking with a script.
Now, when the `exec` method of the bake operator is called, the baking
happens synchronously. That means that the operator call will return only
after the baking is done. The `invoke` method has the same behavior as
before. This approach is similar to e.g. `FLUID_OT_bake_all`.
I did notice that calling the invoke method from a script can still result
in a crash sometimes, probably due to conflicting depsgraph evaluations.
That has to be investigated more.
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