The `Transformer` and `Renderer` classes do not
actually need a `sourcePath` value as by the time
they are doing their work we are only working directly
with full absolute paths.
PR Close#29643
We have already removed this concept from the public API. This just cleans it out altogether.
The `targetPath` was an alternative output path to the original `basePath`.
This is not really a very useful concept, since the actual target path
of each output file is more complex and not consistently relative to the `basePath`.
PR Close#29556
