Remove `nvim-linux64.tar.gz` and `nvim.appimage` as maintaining
these is too much work.

Also fix directory names to be consistent.

Problem: No releases for ARM Linux.

Solution: Provide appimages and tarballs for `linux-arm64`. Rename
x86 releases to `linux-x86_64` for consistency.

Problem:
The windows installer did not have the AllUsers property which leads to
the installer being misidentified as per user installer.
Currently the installer already requires administrative privileges and
installs into the system-wide ProgramFiles directory, but the start menu
entry and uninstaller registration are created only for the current user.
Issue: #29885

https://cmake.org/cmake/help/latest/cpack_gen/wix.html#variable:CPACK_WIX_INSTALL_SCOPE

Solution:
With setting CPACK_WIX_INSTALL_SCOPE to "perMachine" the generated msi
installer includes the Property ALLUSERS=1.
Additionally the start menu entries and uninstaller registration will be
created for all users.

fix #25207

The `.wxs` files were copied from
- cmake repo (BSD 3-Clause License)
  https://github.com/Kitware/CMake/blob/master/Utilities/Release/WiX/install_dir.wxs
- wix repo [Microsoft Reciprocal License](https://github.com/wixtoolset/wix3/blob/b40e9a32c24033e11b77baf2c91a704382f898ed/LICENSE.TXT))
  https://github.com/wixtoolset/wix3/blob/b40e9a32c24033e11b77baf2c91a704382f898ed/src/ext/UIExtension/wixlib/WixUI_InstallDir.wxs

#22856 made it possible for the msi installer to perform per-user
installations, which caused problems for users that already had
per-machine installations trying to update (the Windows Installer does
not support major upgrades across installation context, see #22933 and
https://stackoverflow.com/a/15498911). It was then reverted in #22949,
but the scope of the modification to the PATH environment variable was
not reverted.

This will immensely reduce the complexity required to support both
architectures, reduce overall lines of code and unblock follow-up
simplifications.

Neovim QT was originally bundled on Windows as a response to the then
lackluster terminal options. The situation has dramatically changed,
with viable options such as Windows terminal, Alacritty and Wezterm to
name a few. The Windows build no longer needs this special treatment for
neovim to be usable.

Pros:
  - Release builds will be smaller.
  - Less maintenance burden.
  - Clearer separation of responsibility (neovim issues go to the neovim
    repo and neovim-qt issues to the neovim-qt repo).
  - More consistent treatment between platforms.

Cons:
  - Users who've come to expect neovim-qt to be bundled with nvim will
    need to adjust and download neovim-qt from
    https://github.com/equalsraf/neovim-qt instead.
  - Similarly, build scripts will need to be adjusted to reflect this
    change.

Closes https://github.com/neovim/neovim/issues/21209.

Co-authored-by: Christian Clason <c.clason@uni-graz.at>
Co-authored-by: Gregory Anders <greg@gpanders.com>
Co-authored-by: HiPhish <hiphish@posteo.de>
Co-authored-by: Julio B <julio.bacel@gmail.com>
Co-authored-by: T727 <74924917+T-727@users.noreply.github.com>
Co-authored-by: camoz <camoz@users.noreply.github.com>
Co-authored-by: champignoom <66909116+champignoom@users.noreply.github.com>

Revert this change until a proper solution is implemented, such as allowing the
user to select whether to install per-user or per-machine.

Fixes https://github.com/neovim/neovim/issues/22933.