Use ArgumentNullException.ThrowIfNull when supported (#149)

Author: lahma

src/StronglyTypedIds.Templates/string-full.typedid

@@ -14,7 +14,12 @@
 
         public PLACEHOLDERID(string value)
         {
+#if NET7_0_OR_GREATER
+            global::System.ArgumentNullException.ThrowIfNull(value);
+            Value = value;
+#else
             Value = value ?? throw new global::System.ArgumentNullException(nameof(value));
+#endif
         }
 
         public static readonly PLACEHOLDERID Empty = new PLACEHOLDERID(string.Empty);

src/StronglyTypedIds/EmbeddedSources.String.cs

@@ -16,7 +16,12 @@ partial struct PLACEHOLDERID :
     
             public PLACEHOLDERID(string value)
             {
+    #if NET7_0_OR_GREATER
+                global::System.ArgumentNullException.ThrowIfNull(value);
+                Value = value;
+    #else
                 Value = value ?? throw new global::System.ArgumentNullException(nameof(value));
+    #endif
             }
     
             public static readonly PLACEHOLDERID Empty = new PLACEHOLDERID(string.Empty);