Test: Custom workspace terminal shells

[Tyriar]

#19758

• Windows - @dbaeumer
• macOS or Linux - @chrmarti

Users can once again specify terminal shells in workspace settings. It now presents a message when you launch a terminal asking to whitelist, blacklist or ignore the workspace, while opening the default shell in the meantime.

Please test that all the options work as expected, the setting itself is saved in the workspace's local storage using key terminal.integrated.isWorkspaceShellAllowed, you can change/delete it in the Application tab of dev tools.