Add C# 7.3 to language version dropdown.

ICSharpCode.Decompiler/CSharp/CSharpLanguageVersion.cs

@@ -15,6 +15,7 @@ namespace ICSharpCode.Decompiler.CSharp
 		CSharp7 = 7,
 		CSharp7_1 = 701,
 		CSharp7_2 = 702,
+		CSharp7_3 = 703,
 		Latest = 0x7FFFFFFF
 	}
 }

ICSharpCode.Decompiler/DecompilerSettings.cs

@@ -79,6 +79,10 @@ namespace ICSharpCode.Decompiler
 			if (languageVersion < CSharp.LanguageVersion.CSharp7_2) {
 				introduceRefAndReadonlyModifiersOnStructs = false;
 			}
+			if (languageVersion < CSharp.LanguageVersion.CSharp7_3) {
+				//introduceUnmanagedTypeConstraint = false;
+				//...
+			}
 		}
 
 		bool anonymousMethods = true;

ILSpy/Languages/CSharpLanguage.cs

@@ -98,6 +98,7 @@ namespace ICSharpCode.ILSpy
 						new LanguageVersion(Decompiler.CSharp.LanguageVersion.CSharp7.ToString(), "C# 7.0 / VS 2017"),
 						new LanguageVersion(Decompiler.CSharp.LanguageVersion.CSharp7_1.ToString(), "C# 7.1 / VS 2017.3"),
 						new LanguageVersion(Decompiler.CSharp.LanguageVersion.CSharp7_2.ToString(), "C# 7.2 / VS 2017.4"),
+						new LanguageVersion(Decompiler.CSharp.LanguageVersion.CSharp7_3.ToString(), "C# 7.3 / VS 2017.7"),
 					};
 				}
 				return versions;