Centralize Symbol trait behavior as trait binding metadata

[jonathanvdc]

Problem

Symbol trait behavior is real MLIR semantics, but the generator currently handles it with scattered checks for the Symbol trait and the sym_name attribute. This creates special cases in member planning, property emission, and custom assembly rebuilding.

Trait-driven behavior should be represented in a centralized trait binding model.

Current Hotspots

• src/MLIR.Generators/Emitters/Operations/OperationMemberPlanner.cs: maps sym_name to SymbolName
• src/MLIR.Generators/Emitters/Operations/OperationMemberPlanner.cs: suppresses generic sym_name typing in some paths
• src/MLIR.Generators/Emitters/Operations/OperationPropertyEmitter.cs: emits SymbolName
• src/MLIR.Generators/Emitters/AssemblyFormat/BuildCustomAssemblySyntaxEmitter.cs: maps assembly variable sym_name back to SymbolName

Proposed Direction

Introduce trait binding metadata, for example:

public sealed class TraitBindingModel
{
    public string TraitRecordName { get; }
    public IReadOnlyList<GeneratedPropertyBinding> Properties { get; }
    public IReadOnlyList<string> SuppressedAttributeProperties { get; }
    public string? OperationBaseType { get; }
}

The Symbol trait binding would contribute:

• SymbolName property
• backing attribute: sym_name
• storage/public type: string via builtin StringAttr
• suppression of generic SymName
• assembly-format variable alias from sym_name to SymbolName

Acceptance Criteria

• Symbol trait behavior is described in one centralized trait binding location.
• Operation member planning consumes trait bindings instead of checking Symbol directly.
• Operation property emission consumes generated property bindings instead of hardcoding SymbolName.
• Custom assembly syntax rebuild resolves trait-provided aliases without ad hoc sym_name logic.
• Existing symbol operations keep the SymbolName API and avoid duplicate SymName properties.

Suggested Tests

• Generated symbol op exposes SymbolName.
• Generated symbol op does not also expose generic SymName.
• SymbolName getter/setter round-trips through sym_name and builtin StringAttr.
• Custom assembly involving $sym_name rebuilds from SymbolName.
• Non-symbol op with an attribute named sym_name follows normal attribute behavior.

Notes

This issue intentionally keeps the Symbol special case semantically, but moves it out of emitter control flow and into trait metadata.