#4136: Simplify bool-typed if (c) 1 else 0 to c != 0

An IfInstruction tests its condition for non-zero, so a bool-typed
`if (c) ldc.i4 1 else ldc.i4 0` always equals `c != 0`, which
ExpressionTransforms already folds to `c` for bool `c`. Without this
identity the node reached the C# output as `c ? true : false`, or as
`c || 1 == 0` once negated. The lost `??` form is not addressed here.

ICSharpCode.Decompiler/IL/Transforms/ExpressionTransforms.cs

@@ -584,6 +584,17 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 				context.EndStep(matchCondition);
 				return;
 			}
+			if (inst.TrueInst.MatchLdcI4(1) && inst.FalseInst.MatchLdcI4(0)
+				&& inst.InferType(context.TypeSystem).IsKnownType(KnownTypeCode.Boolean))
+			{
+				context.Step("if (c) true else false -> comp(c != 0)", inst);
+				var comp = new Comp(ComparisonKind.Inequality, Sign.None, inst.Condition, new LdcI4(0));
+				comp.AddILRange(inst);
+				inst.ReplaceWith(comp);
+				context.EndStep(comp);
+				comp.AcceptVisitor(this);
+				return;
+			}
 		}
 
 		IfInstruction HandleConditionalOperator(IfInstruction inst)