Improve generated file handling

Generated files like ui files are a special case. They are not existing but the are important the indexing. For the pchs generation we can simply skip any include which contains a generated file. This is suboptimal but otherwise we would need a system there the generated file are written to the file system shop that the compiler can read it. Or we reimplement the pch generation in a way that we don't call the compiler but implement with clang our own pch creator. Then we could set the generated files as memory buffer. But this looks like out of scope.

The indexing needs the generated files but we must make sure that they are already generated. We should not save any location of a symbol in a generated file in the database. Because we usr memory buffer so fast it is not done any way.