Add SwiftLint rule to enforce stack spacing. (#2080)

Xcode 15 changes the default behaviour and given we're always working from designs, we shouldn't rely on it for our layout.

ElementX/Sources/Other/VoiceMessage/EstimatedWaveformView.swift

@@ -124,7 +124,7 @@ private struct WaveformShape: Shape {
 struct EstimatedWaveformView_Previews: PreviewProvider, TestablePreview {
     static var previews: some View {
         // Wrap the WaveformView in a VStack otherwise the preview test will fail (because of Prefire / GeometryReader)
-        VStack {
+        VStack(spacing: 0) {
             EstimatedWaveformView(waveform: EstimatedWaveform.mockWaveform, progress: 0.5)
                 .frame(width: 140, height: 50)
         }

ElementX/Sources/Other/VoiceMessage/VoiceMessageButton.swift

@@ -110,12 +110,12 @@ extension VoiceMessageButton.State {
 
 struct VoiceMessageButton_Previews: PreviewProvider, TestablePreview {
     static var previews: some View {
-        VStack {
-            HStack {
+        VStack(spacing: 8) {
+            HStack(spacing: 8) {
                 VoiceMessageButton(state: .paused, size: .small, action: { })
                 VoiceMessageButton(state: .paused, size: .medium, action: { })
             }
-            HStack {
+            HStack(spacing: 8) {
                 VoiceMessageButton(state: .playing, size: .small, action: { })
                 VoiceMessageButton(state: .playing, size: .medium, action: { })
             }