fix: memory leak in extension features tab

[SimonSiefke]

Fix an event listener leak in the extensions editor features tab.

Event listeners (before)

One end-to-end test showed an auxclick and keydown event listener leak from markdownRenderer.ts.

{
  "eventListenersWithStackTrace": [
    {
      "type": "auxclick",
      "description": "n=>this.a.fire(n)",
      "objectId": "-6737128020740298089.4.35825",
      "stack": [
        "listener (file:///workspace/vscode-memory-leak-finder/.vscode-test/vscode-linux-x64-1.102.0/resources/app/out/vs/workbench/workbench.desktop.main.js:69:53100)",
        "Object.onWillAddFirstListener (vscode-file://vscode-app/workspace/vscode-memory-leak-finder/.vscode-test/vscode-linux-x64-1.102.0/resources/app/out/vs/workbench/workbench.desktop.main.js:70:53162)",
        "u (vscode-file://vscode-app/workspace/vscode-memory-leak-finder/.vscode-test/vscode-linux-x64-1.102.0/resources/app/out/vs/workbench/workbench.desktop.main.js:29:1565)",
        "vscode-file://vscode-app/workspace/vscode-memory-leak-finder/.vscode-test/vscode-linux-x64-1.102.0/resources/app/out/vs/workbench/workbench.desktop.main.js:27:6613",
        "Array.map (<anonymous>)",
        "vscode-file://vscode-app/workspace/vscode-memory-leak-finder/.vscode-test/vscode-linux-x64-1.102.0/resources/app/out/vs/workbench/workbench.desktop.main.js:27:6605",
        "b0 (vscode-file://vscode-app/workspace/vscode-memory-leak-finder/.vscode-test/vscode-linux-x64-1.102.0/resources/app/out/vs/workbench/workbench.desktop.main.js:384:2706)",
        "Yxe.r (vscode-file://vscode-app/workspace/vscode-memory-leak-finder/.vscode-test/vscode-linux-x64-1.102.0/resources/app/out/vs/workbench/workbench.desktop.main.js:2126:72)",
        "Yxe.n (vscode-file://vscode-app/workspace/vscode-memory-leak-finder/.vscode-test/vscode-linux-x64-1.102.0/resources/app/out/vs/workbench/workbench.desktop.main.js:2111:336)"
      ],
      "count": 194,
      "originalStack": [
        "file:/Users/cloudtest/vss/_work/1/s/src/vs/base/browser/event.ts:40:14"
      ],
      "originalName": "e"
    },
    {
      "type": "keydown",
      "description": "b=>{const v=new yi(b);!v.equals(10)&&!v.equals(3)||K$t(i,e,v)}",
      "objectId": "-6737128020740298089.4.35827",
      "stack": [
        "listener (file:///workspace/vscode-memory-leak-finder/.vscode-test/vscode-linux-x64-1.102.0/resources/app/out/vs/workbench/workbench.desktop.main.js:383:2826)",
        "new N5i (vscode-file://vscode-app/workspace/vscode-memory-leak-finder/.vscode-test/vscode-linux-x64-1.102.0/resources/app/out/vs/workbench/workbench.desktop.main.js:32:8619)",
        "K (vscode-file://vscode-app/workspace/vscode-memory-leak-finder/.vscode-test/vscode-linux-x64-1.102.0/resources/app/out/vs/workbench/workbench.desktop.main.js:32:8780)",
        "b0 (vscode-file://vscode-app/workspace/vscode-memory-leak-finder/.vscode-test/vscode-linux-x64-1.102.0/resources/app/out/vs/workbench/workbench.desktop.main.js:384:2813)",
        "Yxe.r (vscode-file://vscode-app/workspace/vscode-memory-leak-finder/.vscode-test/vscode-linux-x64-1.102.0/resources/app/out/vs/workbench/workbench.desktop.main.js:2126:72)",
        "Yxe.n (vscode-file://vscode-app/workspace/vscode-memory-leak-finder/.vscode-test/vscode-linux-x64-1.102.0/resources/app/out/vs/workbench/workbench.desktop.main.js:2111:336)",
        "Yxe.render (vscode-file://vscode-app/workspace/vscode-memory-leak-finder/.vscode-test/vscode-linux-x64-1.102.0/resources/app/out/vs/workbench/workbench.desktop.main.js:2109:24451)",
        "Cat.H (vscode-file://vscode-app/workspace/vscode-memory-leak-finder/.vscode-test/vscode-linux-x64-1.102.0/resources/app/out/vs/workbench/workbench.desktop.main.js:2126:9844)",
        "Cat.t (vscode-file://vscode-app/workspace/vscode-memory-leak-finder/.vscode-test/vscode-linux-x64-1.102.0/resources/app/out/vs/workbench/workbench.desktop.main.js:2126:8377)"
      ],
      "count": 97,
      "originalStack": [
        "file:/Users/cloudtest/vss/_work/1/s/src/vs/base/browser/markdownRenderer.ts:189:87"
      ],
      "originalName": "e"
    }
  ],
  "isLeak": true
}

After checking where the markdownRenderer connects to the extensionFeatures module, one suspicious disposable from below was discovered. The change registers renderer.render(this.manifest) as a disposable so that it can be properly disposed.

Event listeners (after)

Running the same test again with the fix in place shows no more leaking event listeners

{
  "eventListeners": [],
  "isLeak": false
}