[Feature Request] Rename Instance / ActivityInstance / WorkflowInstance to wrappers

Is your feature request related to a problem? Please describe.

In InvokeActivity::handle

$context = $context->withInstance($instance->getContext())

This is confusing.

ActivityProtoType::getInstance and ActivityProtoType::withInstance are very confusing because the word "instance" means a different thing in these methods.

Describe the solution you'd like

1. Rename Instance to InstanceWrapper, same for ActivityInstance and WorkflowInstance.
2. Rename ActivityInstance::$context to ActivityInstanceWrapper::$instance, same for WorkflowInstance.

and change the relevant getters as well. The code above would change to

$context = $context->withInstance($instanceWrapper->getInstance())

That's much more intuitive, isn't it?

ActivityPrototype::getInstance becomes getInstanceWrapper, which, again, I believe to be much more clear.

Additional context

I could submit a PR if this suggestion is something you like.

Start at InvokeActivity::handle and inspect ActivityProtoType::getInstance, ActivityProtoType::withInstance, ActivityInstance, and WorkflowInstance to map the current instance and context terminology. Done means the requested wrapper names, fields, and relevant getters are updated consistently without changing behavior across their uses.