Port StorageThreadMsg to GenericChannel (#38932)

This change includes the following additions to GenericChannel:
- Add a GenericSend trait which is meant to replace the `IpcSend` trait
over time, as channels are migrated. For the time being this means, that
we often need to use `GenericSend::send()` to disambiguate from the
`IpcSend::send` function, until all usages of `IpcSend` have been
replaced.
- Add an OpaqueSender impl for GenericSender
- Add a profiled version of GenericChannel. The profiling is 1:1 the
same as for the existing profiled IPC channel, namely that only the
blocked time during `recv` is measured.


Testing: No functional changes, covered by existing tests
Part of #38912

---------

Signed-off-by: Jonathan Schwender <schwenderjonathan@gmail.com>

components/shared/net/storage_thread.rs

@@ -2,6 +2,7 @@
  * 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 base::generic_channel::GenericSender;
 use base::id::WebViewId;
 use ipc_channel::ipc::IpcSender;
 use malloc_size_of_derive::MallocSizeOf;
@@ -31,7 +32,7 @@ pub enum StorageThreadMsg {
     ),
 
     /// Gets the available keys in the associated storage data
-    Keys(IpcSender<Vec<String>>, StorageType, WebViewId, ServoUrl),
+    Keys(GenericSender<Vec<String>>, StorageType, WebViewId, ServoUrl),
 
     /// gets the value associated with the given key in the associated storage data
     GetItem(