Add cross-platform support for the new menuinst

[jaimergp]

Changes:

• Use the new menuinst (draft) to create shortcuts in all platforms.
• Make sure conda-standalone is always named _conda.exe
• Use conda/conda#11035's --shortcuts-only
• Provide GUI and CLI options to enable or disable shortcut creation across environments.
  • Windows GUI
  • MacOS PKG (tests pending)
  • Shell installer (tests pending)
• Allow installer creators to disable shortcut functionality all together by setting ALL menu_packages entries to []. This is a bit confusing I think, so we might need to rethink it.
• Ensure .nonadmin files are created for all-users installations in all OS (see discussion at MENU_ITEM_LOCATION is incorrect for all-user installation on macOS menuinst#137)
• Add tests

[jaimergp]

I am starting to sync this branch to main, adding some UI on top to follow the developments with the pre/post install scripts. This requires a new menuinst and a new conda, so most tests will fail for now. Do not review yet :)

[jaimergp]

@conda/constructor - this is finally ready for review! It will require conda-standalone 23.11.0, which is available as a nightly but not released yet. I'll wait to release it til this PR is merged, in case we find something we want to change there. Thanks in advance!

[marcoesters]

Nightlies passing as expected. For some reason, while conda-standalone 23.10 is able to create the miniforge shortcuts (v1), it fails to delete them despite using the same NSIS code. Interestingly, in #740 it succeeds, so maybe there's something about the changes in _nsis.py that make it fail? Looking into it, I had introduced a bug in conda-standalone, where we pass the same value to both prefix and root_prefix. This creates a discrepancy between creation time conditions and removing time conditions, since menuinst v1 calculates different file names.

This conda-standalone <=23.10 bug only would only affect removal of menuinst v1 shortcuts if the installer was created with a constructor version including this PR, but bundling a conda-standalone 23.10 or older. Since it would be hard to debug (I spent a few hours between yesterday and today), I'll require conda-standalone 23.11.0.

There is another possible explanation for the shortcut problems: conda/conda#13338

I've seen this happen when you install and then remove an installation without installing anything into the base environment.

[hoechenberger]

Awesome!