v6.0.0-alpha.10 release of PowerShell

With 311 non-merge commits since v6.0.0-alpha.9,
here are the major changes:

- Fix passing escaped double quoted spaces to native executables
- Add Dockerfiles to build each Linux distribution
- `~/.config/PowerShell` capitalization bug fixed
- Fix crash on Windows 7
- Fix remote debugging on Windows client
- Fix multi-line input with redirected stdin
- Add PowerShell to `/etc/shells` on installation
- Fix `Install-Module` version comparison bug
- Spelling fixes
