The big constants rewrite
Fix #75746, #75685 and more
As a side effect saved 1MB for MWF ;-)
* attribute.cs (GetAttributeArgumentExpression): Use ToType, GetTypedValue.
(GetMarshal, GetMethodImplOptions, GetLayoutKindValue): Values are not
enum based for corlib compilation.
* cfold.cs (BinaryFold): Convert operand for enum additions. Fixed enum
subtractions.
* class.cs (FixedField.Define): Use ResolveAsConstant.
* const.cs (IConstant): Interface constants and enums.
(Const.ResolveValue): New method for constant resolvning.
(ExternalConstant): Constants from imported assemblies.
* constant.cs (Constant.GetTypedValue): Used to get constant with forced
conversion; like enums.
(Constant.ToType): Converts this constant to different type.
(Constant.Increment): Adds 1.
* convert.cs (ImplicitConversionRequired): Simplified.
* cs-parser.jay: Create EnumMember directly.
* decl.cs (MemberCore.CheckObsoleteness): Checks for ObsoleteAttribute presence.
* doc.cs (GenerateEnumDocComment): Removed.
* ecore.cs (Expression.ResolveAsConstant): New constant specific method.
(ConvertIntLiteral): Removed.
(FieldExpr.ResolveMemberAccess): Refactored to remove constant specific if(s).
* enum.cs (EnumMember): Implement IConstant.
(Enum.IsValidEnumConstant): Removed.
(Enum.GetNextDefaultValue): Removed.
(Enum.FindMembers): Updated.
(Enum.GenerateDocComment): Iterate enum members.
* expression.cs (Cast.TryReduce): Handle enums correctly.
(New.Constantify): Made public.
(MemberAccess.DoResolve): Removed contant specific if(s).
* literal.cs (NullLiteral): Implement new abstract methods.
* statement.cs (GotoCase.Resolve): Use new constant methods.
(SwitchLabel.ResolveAndReduce): Use new constant methods.
* typemanager.cs (LookupEnum): Removed.
(IsEnumType): Fixed to work with corlib.
(RegisterConstant): Removed.
(LookupConstant): Removed.
(GetConstant): Changed to work with IConstant.
svn path=/trunk/mcs/; revision=48416
