'make dist' from a test branch with this patch is failing with an error message indicating metainfo.xml files to blame.
Not much of the previous version remains - no point to list changes. It makes more sense to consider this as a new implementation.
Let's move .metainfo.xml.in -> .metainfo.xml generation out from configure, to a separate script.
- It's easier to adjust such a script for future .xml.in -> .xml conversion needs than configure substitutions (this is why I think we will likely need this even to S3_0, and certainly to S3_1)
- Also meson based build can use such a common script