The following code is instantiating one Loader per DevToolsFrameChild instance:
https://searchfox.org/mozilla-central/rev/9902932742fcdce2c956eeb81fd38350f5394ab2/devtools/server/connectors/js-window-actor/DevToolsFrameChild.jsm#319-323

    this.useCustomLoader = this.document.nodePrincipal.isSystemPrincipal;
      this.loader = this.useCustomLoader
        ? new Loader.DevToolsLoader({
            invisibleToDebugger: true,
          })
        : Loader;

This only happens when debugging system principal documents.

This typically happens when opening the Browser Toolbox, where we will load actors once per WindowGlobal.

We were instantiating one new Loader per DevToolsFrameChild instance.
This patch tries to share this loader with all the instances as well as share it
with the one used to load DevToolsServer when we are running in the parent process.

This rule was matching any function prefixed with use, even in modules
that weren't React components.
In addition to that, DevTools aren't using React hooks, so this rule is uncessary.

This helps simplify DevToolsFrameChild and avoid registering and not leaking a connectionchange listener.

This also help always nullify this.loader in DevToolsFrameChild.
For some reason, the first time didDestroy is called, there is still another connection registered in the server.

https://hg.mozilla.org/mozilla-central/rev/7d217a3bec55
https://hg.mozilla.org/mozilla-central/rev/713a550b2bf1
https://hg.mozilla.org/mozilla-central/rev/6f3b3d8024c3