Allow multiple outputs from configure_file, or a similar method

[mitchgrout]

( Relates to #12424 )

The tools that I use to generate my files will emit several files in one go, think paired source/header files. With the current design of configure_file, the command I run will successfully create both source and header, but I can only indicate that one of these files is being created. I can hack my way around this by claiming that I am generating a source, and having the header be generated for free, but it falls apart when I use configure_file to generate multiple sources.

A thought is to allow configure_file to express the configuration of multiple files in one step by changing the output parameter from str to str | list[str] or similar. Or perhaps, this could be a separate method entirely?