fix: propagate execArgv (#5510)

* Use fork instead of spawn

We no longer do in-place updating so no need for the spawn.  The
advantage of a fork is that it preserves flags like --prof which you can
use to profile code-server.

Also I am not sure the comment about not being able to reload in place
with fork was even true to begin with.

* Refresh heartbeat patch

Seems to have gotten out of date a little.

* Propagate execArgv to extension host

This will let us profile the extension host.

patches/heartbeat.diff

@@ -15,7 +15,7 @@ Index: code-server/lib/vscode/src/vs/base/parts/ipc/common/ipc.net.ts
  
  export const enum SocketDiagnosticsEventType {
  	Created = 'created',
-@@ -828,6 +829,19 @@ export class PersistentProtocol implemen
+@@ -829,6 +830,19 @@ export class PersistentProtocol implemen
  		this._socketDisposables.push(this._socketWriter);
  		this._socketReader = new ProtocolReader(this._socket);
  		this._socketDisposables.push(this._socketReader);