Initial IndexedDB Support (#33044)

Adds indexeddb support to servo. At the moment heed is being used as the
backend, although this can be swapped out by implementing `KvsEngine`.
This PR adds a thread + a thread pool for Indexeddb related operations.
Also `database_access_task_source` is added for Indexeddb related
operations.

This is a partial rewrite of #25214. (Reopened due to branching issue)

Fixes #6963

---------

Signed-off-by: Ashwin Naren <arihant2math@gmail.com>
Signed-off-by: Josh Matthews <josh@joshmatthews.net>
Co-authored-by: Rasmus Viitanen <rasviitanen@gmail.com>
Co-authored-by: Josh Matthews <josh@joshmatthews.net>

components/net/indexeddb/engines/mod.rs

@@ -0,0 +1,73 @@
+/* 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::collections::VecDeque;
+
+use ipc_channel::ipc::IpcSender;
+use net_traits::indexeddb_thread::{AsyncOperation, IndexedDBTxnMode};
+use tokio::sync::oneshot;
+
+pub use self::heed::HeedEngine;
+
+mod heed;
+
+#[derive(Eq, Hash, PartialEq)]
+pub struct SanitizedName {
+    name: String,
+}
+
+impl SanitizedName {
+    pub fn new(name: String) -> SanitizedName {
+        let name = name.replace("https://", "");
+        let name = name.replace("http://", "");
+        // FIXME:(arihant2math) Disallowing special characters might be a big problem,
+        // but better safe than sorry. E.g. the db name '../other_origin/db',
+        // would let us access databases from another origin.
+        let name = name
+            .chars()
+            .map(|c| match c {
+                'A'..='Z' => c,
+                'a'..='z' => c,
+                '0'..='9' => c,
+                '-' => c,
+                '_' => c,
+                _ => '-',
+            })
+            .collect();
+        SanitizedName { name }
+    }
+}
+
+impl std::fmt::Display for SanitizedName {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "{}", self.name)
+    }
+}
+
+pub struct KvsOperation {
+    pub sender: IpcSender<Option<Vec<u8>>>,
+    pub store_name: SanitizedName,
+    pub operation: AsyncOperation,
+}
+
+pub struct KvsTransaction {
+    pub mode: IndexedDBTxnMode,
+    pub requests: VecDeque<KvsOperation>,
+}
+
+pub trait KvsEngine {
+    fn create_store(&self, store_name: SanitizedName, auto_increment: bool);
+
+    fn delete_store(&self, store_name: SanitizedName);
+
+    #[expect(dead_code)]
+    fn close_store(&self, store_name: SanitizedName);
+
+    fn process_transaction(
+        &self,
+        transaction: KvsTransaction,
+    ) -> oneshot::Receiver<Option<Vec<u8>>>;
+
+    fn has_key_generator(&self, store_name: SanitizedName) -> bool;
+}