`ClassId` denotes how class is nested; however, you can find
`foo/bar/Outer.Nested` class by `ClassId(foo/bar/Outer/Nested)`. This
will lead to inconsistencies when working with class symbol later
This is also important to `FirQualifierResolverImpl::resolveSymbol`
which detects correct `ClassId` by traversing all symbol qualifiers
We check only `relativeClassName`, because we want to be able to find
classes without package specified
Also, fix test data of resolve tests that have been passing because of
check absence
Roman Golyshev
f00e5b1992