Configure parser lookahead

[spoenemann]

Chevrotain allows to configure a maximum lookahead number globally or per alternative:
https://chevrotain.io/docs/guide/initialization_performance.html#use-a-smaller-global-maxlookahead

We should try to compute a required lookahead for every alternative. Ideally this would happen statically when the CLI runs, so we need to store the information somehow. For example, we could add a property to Alternatives in the grammar and put a value for that property in the CLI. Then the property would be included in the serialized grammar.

We should also allow to configure Chevrotain's IParserConfig, for example as part of our LangiumConfig, so users can change the global maxLookahead.

[spoenemann]

Global config > v0.2.0, fine-grained config > v0.3.0

[spoenemann]

Reopening for the fine-grained config.

[spoenemann]

We should wait for the result of Chevrotain/chevrotain#1714: maybe we won't need any fixed lookahead anymore.