chore: added editorconfig into solution items

Author: pictos

reference/SimpleCalc/MVVM-Xaml/SimpleCalculator.sln

@@ -24,6 +24,7 @@ Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "SimpleCalculator.Tests", "S
 EndProject
 Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "Solution Items", "Solution Items", "{BADA71DC-7FFD-4EDC-9F28-FB74AEADC713}"
 	ProjectSection(SolutionItems) = preProject
+		.editorconfig = .editorconfig
 		.gitignore = .gitignore
 		Directory.Build.props = Directory.Build.props
 		Directory.Build.targets = Directory.Build.targets