Update CS8618 message (#72756)

* Update CS8618 message

* Update ALL comments using the new wording

src/Analyzers/CSharp/CodeFixes/MakeMemberRequired/CSharpMakeMemberRequiredCodeFixProvider.cs

@@ -24,7 +24,7 @@ namespace Microsoft.CodeAnalysis.CSharp.CodeFixes.MakeMemberRequired;
 [ExtensionOrder(Before = PredefinedCodeFixProviderNames.DeclareAsNullable)]
 internal sealed class CSharpMakeMemberRequiredCodeFixProvider : SyntaxEditorBasedCodeFixProvider
 {
-    private const string CS8618 = nameof(CS8618); // Non-nullable variable must contain a non-null value when exiting constructor. Consider declaring it as nullable.
+    private const string CS8618 = nameof(CS8618); // Non-nullable variable must contain a non-null value when exiting constructor. Consider adding the required modifier or declaring it as nullable.
 
     [ImportingConstructor]
     [Obsolete(MefConstruction.ImportingConstructorMessage, error: true)]

src/Compilers/CSharp/Portable/CSharpResources.resx

@@ -5717,10 +5717,10 @@ To remove the warning, you can use /reference instead (set the Embed Interop Typ
     <value>Nullability of reference types in type of parameter doesn't match implemented member (possibly because of nullability attributes).</value>
   </data>
   <data name="WRN_UninitializedNonNullableField" xml:space="preserve">
-    <value>Non-nullable {0} '{1}' must contain a non-null value when exiting constructor. Consider declaring the {0} as nullable.</value>
+    <value>Non-nullable {0} '{1}' must contain a non-null value when exiting constructor. Consider adding the required modifier or declaring the {0} as nullable.</value>
   </data>
   <data name="WRN_UninitializedNonNullableField_Title" xml:space="preserve">
-    <value>Non-nullable field must contain a non-null value when exiting constructor. Consider declaring as nullable.</value>
+    <value>Non-nullable field must contain a non-null value when exiting constructor. Consider adding the required modifier or declaring as nullable.</value>
   </data>
   <data name="WRN_NullabilityMismatchInAssignment" xml:space="preserve">
     <value>Nullability of reference types in value of type '{0}' doesn't match target type '{1}'.</value>