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Seems to have gotten out of date a little.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/series

@@ -21,3 +21,4 @@ telemetry.diff
 display-language.diff
 cli-window-open.diff
 heartbeat.diff
+exec-argv.diff