Allow terminal minimum contrast ratio setting to change luminance the other way

[vscodenpa]

Current behavior of dark selection on dark text:

Repro with these settings:

  "workbench.colorCustomizations": {
    "terminal.selectionBackground": "-010101",
    "terminal.foreground": "-000000",
    "terminal.background": "-eeeeee",
  }

Desire is to invert in this case: