Emit concrete OperationBodySyntax subclass per operation with declarative assembly format

[Copilot]

DialectSourceEmitter previously had no CST representation for operations with declarative assembly formats — only an IOperationAssemblyFormat stub. This adds a generated {ClassName}BodySyntax : OperationBodySyntax class whose fields mirror the token/sub-CST sequence in the operation's AssemblyFormatModel.

Generated class structure

For $lhs ,$rhs attr-dict: type($result), the emitter now produces:

public sealed class MiniArith_AddIOpBodySyntax : OperationBodySyntax
{
    public MiniArith_AddIOpBodySyntax(
        SyntaxToken lhs, SyntaxToken commaToken, SyntaxToken rhs,
        DelimitedSyntaxList<NamedAttributeSyntax> attrDict,
        SyntaxToken colonToken, TypeSyntax resultType) { ... }

    public SyntaxToken Lhs { get; }
    public SyntaxToken CommaToken { get; }
    public SyntaxToken Rhs { get; }
    public DelimitedSyntaxList<NamedAttributeSyntax> AttrDict { get; }
    public SyntaxToken ColonToken { get; }
    public TypeSyntax ResultType { get; }

    public override bool TryGetGenericBody(out GenericOperationBodySyntax? genericBody)
    { genericBody = null; return false; }

    public override void WriteTo(Text.SyntaxWriter writer, int indentLevel,
        System.Action<Text.SyntaxWriter, RegionSyntax, int> writeRegion) { ... }
}

Element-to-field mapping

Format element	Generated C# field type
Punctuation/keyword literal	SyntaxToken
Operand/result variable	SyntaxToken
Attribute variable	AttributeValueSyntax
attr-dict / attr-dict-with-keyword / prop-dict	DelimitedSyntaxList<NamedAttributeSyntax>
regions	IReadOnlyList<RegionSyntax>
type(...)	TypeSyntax
successors / operands	DelimitedSyntaxList<SyntaxToken>

Complex elements (optional groups, oilist, custom directives) are not stored — WriteTo omits them silently for now.

Related change

NamedAttributeSyntax.WriteTo promoted from internal to public so generated consumer assemblies can call it when serialising attribute dictionaries.

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[jonathanvdc]

Great work.