Validate the configuration given to lit-analyzer

[runem]

The configuration given to lit-analyzer is not validated as of now.

First of all, I think the CLI should throw on invalid values, but ts-lit-plugin should only log warnings (no reason to crash when running in the IDE).

Therefore, I think that we should implement one of these solutions:
a. export a validateConfig function that validates the raw, partial config.
b. extend makeConfig with an option to assert values (perhaps a callback that is called on invalid config values).

I also think makeConfig should properly fall back to default values when encountering an invalid value (which it doesn't do for all attributes right now).