text: Title: Support long command line options with hyphens like `--pre-run-modifier`
  Body: To make long option names like `--prerunmodifier` easier to read, Robot handles them case-insensitively so that also `--PreRunModifier` works. This is an old feature and works nicely, but it's inconsistent with the `--my-long-option` format other tools typically use nowadays. We could easily support also that format simply by removing hyphens from long option values at the same time as we convert them to lower case.
  
  Removing hyphens would make `--prerunmodifier`, `--PreRunModifier` and `--pre-run-modifier` all equivalent. It would also allow stupid usages like `--p-r-eru-n-mod-i-fier`, but we support also `--PReruNmodIfier` so it shouldn't be a big deal. The leading two hyphens obviously shouldn't be removed.
  
  Supporting multiple different formats is perhaps not a good idea in general, though, and it could be better to require using a single format instead. I personally prefer the `--my-long-option` format over the other alternatives because it is consistent with shorter options like `--option` and also what other tools typically use. I'm not sure is requiring that worth the deprecation effort, but making that format valid now certainly helps if we ever want to do that.