Fix vector-im/element-x-ios/issues/134 - Prevent home screen room last message attributed string from being computed on every update

Add async/await methods to the AttributedStringBuilder and adopt them throughout the app

ElementX/Sources/Other/HTMLParsing/AttributedStringBuilder.swift

@@ -32,6 +32,12 @@ struct AttributedStringBuilder: AttributedStringBuilderProtocol {
         }
     }
     
+    func fromPlain(_ string: String?) async -> AttributedString? {
+        await Task.detached {
+            fromPlain(string)
+        }.value
+    }
+    
     func fromPlain(_ string: String?) -> AttributedString? {
         guard let string = string else {
             return nil
@@ -44,6 +50,12 @@ struct AttributedStringBuilder: AttributedStringBuilderProtocol {
         return try? AttributedString(mutableAttributedString, including: \.elementX)
     }
     
+    func fromHTML(_ htmlString: String?) async -> AttributedString? {
+        await Task.detached {
+            fromHTML(htmlString)
+        }.value
+    }
+    
     // Do not use the default HTML renderer of NSAttributedString because this method
     // runs on the UI thread which we want to avoid because renderHTMLString is called
     // most of the time from a background thread.