Add Windows install override command

[Mihnea-Teodor Stoica (MihneaTeodorStoica)]

Summary

• Add hidden Windows-only --x-install and --x-uninstall commands.
• Copy the current edit.exe into %ProgramFiles%\Microsoft\Edit as a stable install location.
• Update the machine Path so that stable directory is placed before System32, then broadcast the environment change.

Fixes #829

Validation

• cargo fmt --all -- --check
• cargo check -p edit
• cargo check -p edit --target x86_64-pc-windows-msvc
• cargo clippy -p edit -- --no-deps --deny warnings
• cargo clippy -p edit --target x86_64-pc-windows-msvc -- --no-deps --deny warnings
• cargo test -p edit
• git diff --check

[Leonard Hecker (lhecker)]

Sorry about the wait but I was gone for a while. During that time we made some experience with packaging https://github.com/microsoft/coreutils and found that Inno Setup is pretty neat. I think we may use that for Edit as well. I've ported the coreutils script to Edit already (https://github.com/microsoft/edit/tree/dev/lhecker/iss). It's not 100% settled yet if we'll go with that approach but it's likely.