Avoid shim blocking when running a GUI app

[milnak]

Description

Currently scoop shim will block when running a GUI app.

To repro this, do the following from a powershell console:

scoop install extras/notepad2-zufuliu
notepad2

The console will be blocked until notepad exits.

I have added an environment variable that can be set to override this behavior.

Motivation and Context

Relates to #1606

How Has This Been Tested?

Build shim, verified against notepad2 and console apps.

Checklist:

• I have read the Contributing Guide.
• I have ensured that I am targeting the develop branch.
• I have updated the documentation accordingly.
• I have updated the tests accordingly.
• I have added an entry in the CHANGELOG.

[milnak]

looks like visual studio did some reformatting of the file. If you want me to undo those reformats, let me know and ill push a new iter.

[spider2048]

Using the develop branch (which had #5559 and #5684 merged recently) would solve the issue for every shim type.
So, this is implemented in the develop branch.

But, when a target application uses AttachConsole to obtain console handles, both the current develop branch and your's won't be able to. For instance,

$ scoop config shim scoopcs
$ scoop install alacritty
$ alacritty -V
<blank>
$ &(scoop which alacritty) -V
alacritty 0.12.3 (5efb069)

There is #5721 waiting for approval which would solve this issue.
Because of this, the process can't obtain the handles to console just by using AttachConsole, because the shim exits.

[milnak]

@spider2048 it looks like your changes handle this case and more, so this PR can likely be closed.

[amorphobia]

Since the fix is not released yet (will be in 0.4.0), I provide a workaround for current version (0.3.1).

Save following content as np2.ps1 in your $env:Path:

if ($args.Length -lt 1) {
    Start-Process -WindowStyle hidden notepad2.exe
} else {
    Start-Process -WindowStyle hidden notepad2.exe ($args -join ' ')
}

Just use np2 [file_path] from command line.