Create a BubbleReactionsViewSizer in order to determine reactions view height.

Riot/Modules/Room/BubbleReactions/BubbleReactionsViewSizer.h

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+/*
+Copyright 2020 New Vector Ltd
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+#import <Foundation/Foundation.h>
+#import <UIKit/UIKit.h>
+
+@class BubbleReactionsViewModel;
+
+NS_ASSUME_NONNULL_BEGIN
+
+@interface BubbleReactionsViewSizer : NSObject
+
+// Use Objective-C as workaround as there is an issue affecting UICollectionView sizing. See https://developer.apple.com/forums/thread/105523 for more information.
+- (CGFloat)heightForViewModel:(BubbleReactionsViewModel*)viewModel
+                 fittingWidth:(CGFloat)fittingWidth;
+
+@end
+
+NS_ASSUME_NONNULL_END