Auto merge of #27304 - paulrouget:staticdevtoolsport, r=jdm

UWP: non random port for devtools, and support for custom UWP prefs

packages-prefs.json is now taken into account for libsimpleservo. Making it possible to have custom pref for the UWP builds, removing some weirdness in the way we handle preferences in the hololens code.

This also adds a new set of preferences to control the devtools server startup state, and make the port choice constant across sessions.

Fix #27267
Fix #22970

components/servo/lib.rs

@@ -356,9 +356,15 @@ where
         let mem_profiler_chan = profile_mem::Profiler::create(opts.mem_profiler_period);
 
         let debugger_chan = opts.debugger_port.map(|port| debugger::start_server(port));
-        let devtools_chan = opts
-            .devtools_port
-            .map(|port| devtools::start_server(port, embedder_proxy.clone()));
+
+        let devtools_chan = if opts.devtools_server_enabled {
+            Some(devtools::start_server(
+                opts.devtools_port,
+                embedder_proxy.clone(),
+            ))
+        } else {
+            None
+        };
 
         let coordinates = window.get_coordinates();
         let device_pixel_ratio = coordinates.hidpi_factor.get();