Devtools device description: improve how Servo is advertised in Firefox's about:debugging (fixes #27528) (#32227)

* Devtools device description: fix the case of the 'platformversion' property

* Devtools device description: expose the properties Firefox expects for the display name and version of the server

When connecting to Servo from Firefox (about:debugging), it will display "Servo (71.0)" instead of "{$name} (${version})".

* Devtools device description: update versions to match those in the UA string

* Devtools device description: expose a property (appbuildid) Firefox expects to compare versions for compatibility (_compareVersionCompatibility function)

* Devtools device description: advertise a current platform version to remove the incompatibility warning in Firefox's about:debugging

* Devtools preference actor: fix retrieving the actual preference by its key

* Devtools preference actor: translate Firefox preference names onto the corresponding Servo preference names

* Devtools device description: downgrade the platform version to prevent a confusing warning in about:debugging if the build ID is newer than that of Firefox (likely)

* Devtools device description: add comments

* Devtools device description: use CARGO_PKG_VERSION for the user-visible version number

components/devtools/build.rs

@@ -0,0 +1,20 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
+
+use std::path::Path;
+use std::{env, fs};
+
+use chrono::Local;
+
+fn main() {
+    let path = Path::new(&env::var_os("OUT_DIR").unwrap()).join("build_id.rs");
+    fs::write(
+        path,
+        format!(
+            "const BUILD_ID: &str = \"{}\";",
+            Local::now().format("%Y%m%d%H%M%S")
+        ),
+    )
+    .unwrap();
+}