Hadrian: avoid response files when command line is short enough

The use of response files has harmed the dev experience. See #27230. This MR fixes this by:

• Reduces the use of response files in Hadrian by only using response files when when the command line in long
  • After this change, I've observed only approx. 130 response files on a Windows build.
• Removes the -r / --keep-response-files command line option
  • Now always keep the response files and place them in the _build/rsp dir.

This should simplify the developer experience: without knowing/learning any special command line options devs can manually run commands by copy and pasting from hadrain output. Note I've also confirmed on windows that no response files end up in in bindist dirs after running ./hadrian/build -j binary-dist-dir.