DevTools: Move Source related code to dedicated source.rs file (#36667)

Currently Source related code exists in watcher.rs and thread.rs. This
change moves source-related code to a dedicated source.rs file. This is
in preparation for adding support for showing source code in the
Debugger > Source panel.

- [x] Testing: These changes should not affect current functionality as
it only moves the existing code
- [x] Fixes: part of https://github.com/servo/servo/issues/36027

---------

Signed-off-by: atbrakhi <atbrakhi@igalia.com>

components/devtools/actors/source.rs

@@ -0,0 +1,50 @@
+/* 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::cell::{Ref, RefCell};
+use std::collections::BTreeSet;
+
+use serde::Serialize;
+use servo_url::ServoUrl;
+
+#[derive(Clone, Debug, Eq, Ord, PartialEq, PartialOrd, Serialize)]
+#[serde(rename_all = "camelCase")]
+pub(crate) struct SourceData {
+    pub actor: String,
+    /// URL of the script, or URL of the page for inline scripts.
+    pub url: String,
+    pub is_black_boxed: bool,
+}
+
+#[derive(Serialize)]
+pub(crate) struct SourcesReply {
+    pub from: String,
+    pub sources: Vec<SourceData>,
+}
+
+pub(crate) struct Source {
+    actor_name: String,
+    source_urls: RefCell<BTreeSet<SourceData>>,
+}
+
+impl Source {
+    pub fn new(actor_name: String) -> Self {
+        Self {
+            actor_name,
+            source_urls: RefCell::new(BTreeSet::default()),
+        }
+    }
+
+    pub fn add_source(&self, url: ServoUrl) {
+        self.source_urls.borrow_mut().insert(SourceData {
+            actor: self.actor_name.clone(),
+            url: url.to_string(),
+            is_black_boxed: false,
+        });
+    }
+
+    pub fn sources(&self) -> Ref<BTreeSet<SourceData>> {
+        self.source_urls.borrow()
+    }
+}