Watch configuration provider for updates

[Lars Reimann]

We have an external tool to run compiled DSL code. It is part of our language server, since it is also needed for validation $^1$. The tool gets started with some CLI command.

When used from VS Code, this command is configured via a setting. If the tool could not be started and the setting is updated, we want to try again with the updated setting.

➡️ For this, it would be nice if the ConfigurationProvider would emit an event after an update has happened.

We're currently overriding the type and the implementation of the ConfigurationProvider in our shared module, but this seems like functionality that could be useful elsewhere.

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$^1$ In particular, we want to compute the schema of tabular data when we first load it. Schemata of derived data can then get computed statically.