Include type info for unknown packages

[isergieienkov]

builtin package is non detected (maybe some others too) which results in missing both package and type info in match string. I propose to keep as much info as possible. Should allow matching of builtin type functions too. For example: var err error err.Error() -----> results in .Error match string. With this change it will be .error.Error

[ashanbrown]

@isergieienkov Thanks for your proposal and sorry for not reviewing it sooner. Is it possible to write a test for this behavior so I can better understand the issue? As I understand it, you'd like to forbid some identifiers in the builtin package. Thanks.

[isergieienkov]

Added test for this case