Support for configuring and specifying multiple different shells in Integrated Terminal

[gharabed]

While it is possible to run multiple different shells (bash, python, powershell, cmd, etc.) at the same time in the Integrated Terminal, it is more difficult to start them than it should be. Even the "Shell Launcher" extension, while better, is still not optimal. As a user, I should be able to configure the different shells I want in the User Settings and then when I click on the "+" icon to add a new shell, I should be presented with a popup list with all of the configured terminals. So in the user settings, I would replace the "terminal.integrated.shell.windows" string value with an array:

"terminal.integrated.shell.windows": : [
        {
            "shell": "c:\\Windows\\system32\\cmd.exe",
            "label": "cmd"
        },
        {
            "shell": "C:\\Program Files\\Git\\bin\\bash.exe",
            "label": "Git bash"
        },
        {
            "shell": "C:\\Users\\johnsmith\\AppData\\Local\\Programs\\Python\\Python37\\python.exe",
            "label": "Python 3.7"
        }
    ]

and when clicking on the "+" symbol, pop up a list of the labels.

[vscodebot]

(Experimental duplicate detection)
Thanks for submitting this issue. Please also check if it is already covered by an existing one, like:

• Create new terminal with a shell other than default without changing default (#80813)

[NotWearingPants]

/duplicate #45444