Add removeHandler(context: ChannelHandlerContext) to SynchronousOperations of ChannelPipeline (#2912)

### Motivation:

As per #2906.

### Modifications:

Added a method to SynchrounousOperations of ChannelPipeline.

### Result:

Now we are able to remove channel handlers by context.

---------

Co-authored-by: Franz Busch <[email protected]>

Author: supersonicbyte

Sources/NIOCore/ChannelPipeline.swift

@@ -1161,6 +1161,17 @@ extension ChannelPipeline {
             return promise.futureResult
         }
 
+        /// Remove a `ChannelHandler` from the `ChannelPipeline`.
+        ///
+        /// - parameters:
+        ///     - context: the `ChannelHandlerContext` that belongs to `ChannelHandler` that should be removed.
+        /// - returns: the `EventLoopFuture` which will be notified once the `ChannelHandler` was removed.
+        public func removeHandler(context: ChannelHandlerContext) -> EventLoopFuture<Void> {
+            let promise = self.eventLoop.makePromise(of: Void.self)
+            self._pipeline.removeHandler(context: context, promise: promise)
+            return promise.futureResult
+        }
+
         /// Returns the `ChannelHandlerContext` for the given handler instance if it is in
         /// the `ChannelPipeline`, if it exists.
         ///

Tests/NIOPosixTests/ChannelPipelineTest.swift

@@ -1119,6 +1119,51 @@ class ChannelPipelineTest: XCTestCase {
         }
     }
 
+    func testRemovingByContexSync() throws {
+        class Handler: ChannelInboundHandler, RemovableChannelHandler {
+            typealias InboundIn = Never
+
+            var removeHandlerCalled = false
+            var withinRemoveHandler = false
+
+            func removeHandler(context: ChannelHandlerContext, removalToken: ChannelHandlerContext.RemovalToken) {
+                self.removeHandlerCalled = true
+                self.withinRemoveHandler = true
+                defer {
+                    self.withinRemoveHandler = false
+                }
+                context.leavePipeline(removalToken: removalToken)
+            }
+
+            func handlerRemoved(context: ChannelHandlerContext) {
+                XCTAssertTrue(self.removeHandlerCalled)
+                XCTAssertTrue(self.withinRemoveHandler)
+            }
+        }
+
+        let channel = EmbeddedChannel()
+        defer {
+            XCTAssertNoThrow(XCTAssertTrue(try channel.finish().isClean))
+        }
+        let allHandlers = [Handler(), Handler(), Handler()]
+        XCTAssertNoThrow(try channel.pipeline.addHandler(allHandlers[0], name: "the first one to remove").wait())
+        XCTAssertNoThrow(try channel.pipeline.addHandler(allHandlers[1], name: "the second one to remove").wait())
+        XCTAssertNoThrow(try channel.pipeline.addHandler(allHandlers[2], name: "the last one to remove").wait())
+
+        let firstContext = try! channel.pipeline.syncOperations.context(name: "the first one to remove")
+        let secondContext = try! channel.pipeline.syncOperations.context(name: "the second one to remove")
+        let lastContext = try! channel.pipeline.syncOperations.context(name: "the last one to remove")
+
+        XCTAssertNoThrow(try channel.pipeline.syncOperations.removeHandler(context: firstContext).wait())
+        XCTAssertNoThrow(try channel.pipeline.syncOperations.removeHandler(context: secondContext).wait())
+        XCTAssertNoThrow(try channel.pipeline.syncOperations.removeHandler(context: lastContext).wait())
+
+        for handler in allHandlers {
+            XCTAssertTrue(handler.removeHandlerCalled)
+            XCTAssertFalse(handler.withinRemoveHandler)
+        }
+    }
+
     func testNonRemovableChannelHandlerIsNotRemovable() {
         class NonRemovableHandler: ChannelInboundHandler {
             typealias InboundIn = Never