Test: Quick open/file list performance for large workspaces

[Tyriar]

Test for #55:

• Windows - @isidorn
• OS X - @jrieken
• Linux - @Tyriar

Verify that in a 'large' workspace (e.g., VS Code or Node) with Ctrl+P (Cmd+P):

• Files are found as expected.
• After the progress indicator is gone, keystrokes appending to the search term result in immediate response.
• To quickly do this with the Node sources use a shallow clone: git clone --depth=1 https://github.com/nodejs/node.git