java: remove the extra wrapping of HostContext and pass it directly

[axic]

Depends on #549.

[axic]

The whole point of evmc_host_context is to be an opaque object from the interface perspective, and since it only needs to be valid during the scope of execute I think this change is the correct one.

[atoulme]

I think that's ok, not sure I grasp it entirely. I thought the point of having this organization was to pass the context when doing internal calls, but I think you're saying that's not necessary.

[axic]

I think that's ok, not sure I grasp it entirely. I thought the point of having this organization was to pass the context when doing internal calls, but I think you're saying that's not necessary.

The context is needed for all the host functions, just that we can opaquely pass it around I think. We can only make this simplification because the scope is limited.

[chfast]

Looks nice. I assume that an HostContext object is not going to be garbage collected while being the argument of execute().

[axic]

Looks nice. I assume that an HostContext object is not going to be garbage collected while being the argument of execute().

That is my assumption. We are safe to do this because execute is only executed in a single place where the context's lifetime outlives that of execute, so it won't be collected. And also anything passed to the JNI has a guaranteed lifetime during that JNI call, but not beyond (unless specifically using NewGlobalRef) apparently.