Calculate definitions when requested

[DavyLandman]

In the past we would calculate rascal definitions when they were requested. But since the typechecker was too slow, we disabled this.

It would be nice, for some operations (like goto definition, but not for hover) to start the typechecker in case the makeSummary couldn't find a tpl.

[jurgenvinju]

Agreed. Proposal: check the damage wrt tpl files that have to be recalculated (an over-approximation), by comparing timestamps. If too many are out of date, trigger a large asynchronous build but give an empty or partial answer. If only a few are out of date, trigger the incremental checker and provide the exact answer immediately. This all in client LSP Rascal code, not hard-wired into the framework.