Update IsImplicitlyDeclared doc (#48199)

Closes #48193

src/Compilers/Core/Portable/Symbols/ISymbol.cs

@@ -127,7 +127,7 @@ public interface ISymbol : IEquatable<ISymbol?>
 
         /// <summary>
         /// Returns true if this symbol was automatically created by the compiler, and does not have
-        /// an explicit corresponding source code declaration. 
+        /// an explicit corresponding source code declaration.
         /// </summary> 
         /// <remarks>
         /// This is intended for symbols that are ordinary symbols in the language sense, and may be
@@ -146,6 +146,9 @@ public interface ISymbol : IEquatable<ISymbol?>
         /// <item><description>Methods in anonymous types.</description></item>
         /// </list>
         /// </para>
+        /// <para>
+        /// The class and entry point method for top-level statements are not considered as implicitly declared.
+        /// </para>
         /// </remarks>
         bool IsImplicitlyDeclared { get; }