Fixing a memory leak in getTerminalActionBarArgs by disposing the previous actions when updating the actions.

Before

When opening and closing the panel, many instances of getTerminalActionBarArgs are created:

After

When opening and closing the panel, the number of getTerminalActionBarArgs functions stays constant:

Only a leaking i function or class is remaining, which seems to be related to xterm addon WebGL.

{
  "namedFunctionCount3": [
    {
      "count": 2473,
      "delta": 2377,
      "name": "i",
      "sourceLocation": "vscode-file://vscode-app/home/simon/.cache/repos/vscode/node_modules/@xterm/addon-webgl/lib/addon-webgl.js:0:82918",
      "originalName": null
    }
  ],
  "isLeak": true
}