Show tsconfig.json parsing errors

[hoanhtien]

User should be notified if there are errors in his/her tsconfig.json file.

This will be helpful in cases like #270.

[johnfn]

This would be super helpful. It took me the longest time to realize I had tsconfig errors.

[mhegazy]

@zhengbli this is really a server issue. I would say, if we find a tsconfig, and fail to load it, we should still create a "configuredProject", that has the default configuration, and add the errors to the project, and return them when querying for all errors. currently, we just ignore the tsconfig.json, as if it never existed, and the errors will be gone.