* Allow different names for ...rest
* Resolves#3945
* This change requires an explicit name for the rest argument in `WholeStreamCommand`,
which is why there are so many changed files.
* Remove redundant clone
* Add tests
* Move tests into own file
* Move data structs to own file
* Move functions parsing 1 Token (primitives) into own file
* Rename param_flag_list to signature
* Add tests
* Fix clippy lint
* Change imports to new lexer structure
