Code formatting updates (#4502)

* Editorconfig: Add space_before_self_closing setting

This was a difference between the way dotnet-format and Rider format code. See https://www.jetbrains.com/help/rider/EditorConfig_Index.html

* Editorconfig: Keep 4 spaces indentation for Swagger JSON files

They are all formatted that way, let's keep it like that.

* Apply dotnet-format, mostly white-space related changes

BTCPayServer.Abstractions/Extensions/StringExtensions.cs

@@ -6,7 +6,6 @@ namespace BTCPayServer.Abstractions.Extensions;
 
 public static class StringExtensions
 {
-
     public static bool IsValidFileName(this string fileName)
     {
         return !fileName.ToCharArray().Any(c => Path.GetInvalidFileNameChars().Contains(c)
@@ -41,5 +40,4 @@ public static class StringExtensions
             return str.Substring(0, str.Length - 1);
         return str;
     }
-    
 }