docs: Functional renaming commit for CMake-as-default

docs: Functional renaming commit for CMake-as-default

Rename all the files which will be edited substantially in the next commit, without changing their
contents

Docs will not build for this ocmmit.

This is done so that git doesn't decide we renamed xxx-cmake -> xxx-legacy in the next commit, which
is what it will infer otherwise (and makes rebasing more of a pain than it should be)