Continuous commands stop updating for dynamically loaded languages after rebuilding/reloading the language about spoofax-pie

[Gohla]

Two problems were uncovered while implementing this:

• When a language is dynamically reloaded, the PIE instance is recreated. When it is recreated, its callbacks are lost, and thus even though the task of a continuous command is re-executed, there is no callback to inform the IDE of the new feedback. Therefore, the editor with feedback is not updated.
• Certain language tasks require their definition files. For example, the parse task of a language requires its parse table, such that it is re-executed when the parse table changes. However, this dependency is made to the local file of that definition resource. The problem is that in Eclipse, we use Eclipse resources, and these do not match the local file requirements. For example, when an SDF3 file of the language is changed, and thus the parse table of the language is updated, the Eclipse resource of that parse table is provided, while the parse task requires it as a local resource. Therefore, changes to the parse table do not trigger re-execution of parse tasks. The same problem exists with other tasks as well.

[Gohla]

Fixed by 881f866