Fix #3820: decompile dynamic ~ as ~x instead of an unsupported-opcode error

VisitDynamicUnaryOperatorInstruction handled every dynamic unary operator
except ExpressionType.OnesComplement, so ~x on a dynamic operand fell through
to the unsupported-opcode error expression and produced uncompilable output
(an incomplete cast that fails to parse). Map it to the bitwise-complement
operator, like the sibling unary cases.

Assisted-by: Copilot:claude-opus-4.8:GitHub Copilot CLI

ICSharpCode.Decompiler.Tests/TestCases/Pretty/DynamicTests.cs

@@ -394,6 +394,7 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 			//++a;
 			DynamicTests.Casts(-a);
 			DynamicTests.Casts(+a);
+			DynamicTests.Casts(~a);
 		}
 
 		private static void Loops(dynamic list)

ICSharpCode.Decompiler/CSharp/ExpressionBuilder.cs

@@ -4540,6 +4540,8 @@ namespace ICSharpCode.Decompiler.CSharp
 					return CreateUnaryOperator(UnaryOperatorType.Minus, isChecked: true);
 				case ExpressionType.UnaryPlus:
 					return CreateUnaryOperator(UnaryOperatorType.Plus, isChecked: inst.BinderFlags.HasFlag(CSharpBinderFlags.CheckedContext));
+				case ExpressionType.OnesComplement:
+					return CreateUnaryOperator(UnaryOperatorType.BitNot);
 				case ExpressionType.IsTrue:
 					var operand = TranslateDynamicArgument(inst.Operand, inst.OperandArgumentInfo);
 					Expression expr;