only read existing source files when inferring version identifiers ...

- i.e. leave out auto-generated sources like unittest runners
- also skip linker files

update changelog to fully explain the feature

Added experimental build settings to filter applicable version identifiers ...

Those settings allow to filter version identifiers and debug version identifiers
used during building a package. This can improve the build cache efficiency for
libraries that are used by multiple applications with different version
identifiers.

- only merge filters from source dependencies when the
  dependent has an explicit filter list as well