message: Improve keybinding JSON schema
  The pattern regex now correctly disallows keybindings consisting of only
  modifiers, modifiers not separated by "+", and unknown keys. Certain
  shift+numpad combinations are also not allowed.
  The description lists allowed key names in tabular format (assuming the
  client renders \t correctly).
diff: "title": "Microsoft's Windows Terminal Settings Profile Schema'",
  "definitions": {
  "KeyChordSegment": {
  - "pattern": "^(?<modifier>(ctrl|alt|shift)\\+?((ctrl|alt|shift)(?<!\\2)\\+?)?((ctrl|alt|shift)(?<!\\2|\\4))?\\+?)?(?<key>[^+\\s]+?)?(?<=[^+\\s])$",
  - "type": "string"
  + "pattern": "^(?<modifier>(ctrl|alt|shift)(?:\\+(ctrl|alt|shift)(?<!\\2))?(?:\\+(ctrl|alt|shift)(?<!\\2|\\3))?\\+)?(?<key>[^\\s+]|backspace|tab|enter|esc|escape|space|pgup|pageup|pgdn|pagedown|end|home|left|up|right|down|insert|delete|(?<!shift.+)(?:numpad_?[0-9]|numpad_(?:period|decimal))|numpad_(?:multiply|plus|add|minus|subtract|divide)|f[1-9]|f1[0-9]|f2[0-4]|plus)$",
  + "type": "string",
  + "description": "The string should fit the format \"[ctrl+][alt+][shift+]<keyName>\", where each modifier is optional, separated by + symbols, and keyName is either one of the names listed in the table below, or any single key character. The string should be written in full lowercase.\nbackspace\tBACKSPACE key\ntab\tTAB key\nenter\tENTER key\nesc, escape\tESC key\nspace\tSPACEBAR\npgup, pageup\tPAGE UP key\npgdn, pagedown\tPAGE DOWN key\nend\tEND key\nhome\tHOME key\nleft\tLEFT ARROW key\nup\tUP ARROW key\nright\tRIGHT ARROW key\ndown\tDOWN ARROW key\ninsert\tINS key\ndelete\tDEL key\nnumpad_0-numpad_9, numpad0-numpad9\tNumeric keypad keys 0 to 9. Can't be combined with the shift modifier.\nnumpad_multiply\tNumeric keypad MULTIPLY key (*)\nnumpad_plus, numpad_add\tNumeric keypad ADD key (+)\nnumpad_minus, numpad_subtract\tNumeric keypad SUBTRACT key (-)\nnumpad_period, numpad_decimal\tNumeric keypad DECIMAL key (.). Can't be combined with the shift modifier.\nnumpad_divide\tNumeric keypad DIVIDE key (/)\nf1-f24\tF1 to F24 function keys\nplus\tADD key (+)"
  },
  "Color": {
  "default": "#",
  