When setting realtime channel options, pass through to REST channel

When calling -[ARTRealtimeChannel setOptions:callback:], the passed
options are not used to update the options of this instance’s REST
channel. This means that, for example, if we update the realtime
channel’s cipher options, these options will not be used to decrypt
messages subsequently fetched using the -history:* methods.

I think this is something we missed when fixing #1207 (34d68ec).

This issue is causing ably/ably-flutter#296.

Closes #1265.

Source/ARTRealtimeChannel.m

@@ -1235,6 +1235,7 @@ - (void)setOptions:(ARTRealtimeChannelOptions *_Nullable)options callback:(nulla
 
 - (void)setOptions_nosync:(ARTRealtimeChannelOptions *_Nullable)options callback:(nullable ARTCallback)callback {
     [self setOptions_nosync:options];
+    [self.restChannel setOptions_nosync:options];
 
     if (!options.modes && !options.params) {
         if (callback)

Spec/Tests/RealtimeClientChannelTests.swift

@@ -4188,6 +4188,39 @@ class RealtimeClientChannelTests: XCTestCase {
         expect(lastAttach.flags & subscribeFlag).to(equal(subscribeFlag))
         expect(lastAttach.params).to(equal(channelOptions.params))
     }
+
+    func test__Channel_options__setOptions__shouldUpdateOptionsOfRestChannel() {
+        let client = AblyTests.newRealtime(AblyTests.commonAppSetup())
+        defer { client.dispose(); client.close() }
+        let channel = client.channels.get("foo")
+
+        waitUntil(timeout: testTimeout) { done in
+            client.connection.once(.connected) { _ in
+                done()
+            }
+        }
+
+        var restChannelSetOptions: ARTChannelOptions?
+        let token = channel.internal.restChannel.testSuite_getArgument(from: #selector(ARTRestChannelInternal.setOptions_nosync(_:)), at: 0) { arg in
+            guard let optionsArg = arg as? ARTChannelOptions else {
+                XCTFail("Expected setOptions: to have been called with an ARTChannelOptions instance")
+                return
+            }
+            restChannelSetOptions = optionsArg
+        }
+        defer { token.remove() }
+
+        let channelOptions = ARTRealtimeChannelOptions(cipherKey: ARTCrypto.generateRandomKey() as NSData)
+
+        waitUntil(timeout: testTimeout) { done in
+            channel.setOptions(channelOptions) { error in
+                XCTAssertNil(error)
+                done()
+            }
+        }
+
+        expect(restChannelSetOptions).to(beIdenticalTo(channelOptions))
+    }
 
     // RTL17
     func test__122__Channel__history__should_not_emit_messages_to_subscribers_if_the_channel_is_in_any_state_other_than_ATTACHED() {