Switch indexeddb backend to sqlite and improve IPC messaging (#38187)

- Use sqlite instead of heed. (one indexed database = one sqlite
database)
- Implement the backend for indexes
- Use keyranges where needed (as specified by the spec)
- Implement `getKey`
- Fix channel error messaging (led to a bunch of changes to how async
requests are handled)

Note: `components/net/indexeddb/engines/sqlite/serialize.rs` is unused;
I can delete it if needed.

Testing: Switching to sqlite eliminated many panics (exposing some new
failures).
Fixes: #38040

---------

Signed-off-by: Ashwin Naren <arihant2math@gmail.com>

components/script/dom/idbtransaction.rs

@@ -229,6 +229,7 @@ impl IDBTransactionMethods<crate::DomTypeHolder> for IDBTransaction {
         // returns the same IDBObjectStore instance.
         let mut store_handles = self.store_handles.borrow_mut();
         let store = store_handles.entry(name.to_string()).or_insert_with(|| {
+            // TODO: get key path from backend
             let store = IDBObjectStore::new(
                 &self.global(),
                 self.db.get_name(),