Deduplicate IObjectNodeWithAlignment into shared Common dependency analysis

[Copilot]

This change removes the duplicate IObjectNodeWithAlignment definitions introduced after #129966 and restores a single shared contract for both AOT compiler projects.

• Shared interface

  • Moves IObjectNodeWithAlignment to src/coreclr/tools/Common/Compiler/DependencyAnalysis/IObjectNodeWithAlignment.cs
  • Uses namespace ILCompiler.DependencyAnalysis, matching the surrounding shared dependency-analysis surface
  • Preserves the XML doc contract that GetAlignment must stay consistent with GetData / GetDehydratableData

• Project file cleanup

  • Updates ILCompiler.Compiler.csproj and ILCompiler.ReadyToRun.csproj to compile the shared Common file
  • Removes the two project-local interface entries

• Consumer impact

  • ReadyToRun now consumes the shared interface through the common namespace instead of a project-local duplicate
  • Existing implementations continue to compile against a single definition without changing behavior

namespace ILCompiler.DependencyAnalysis
{
    public interface IObjectNodeWithAlignment
    {
        int GetAlignment(NodeFactory factory);
    }
}

[Copilot]

Pull request overview

This PR consolidates the IObjectNodeWithAlignment interface into the shared CoreCLR tooling “Common” dependency-analysis source set, removing the duplicated per-project definitions and keeping a single canonical contract for both ILCompiler tool projects.

Changes:

• Add shared ILCompiler.DependencyAnalysis.IObjectNodeWithAlignment under src/coreclr/tools/Common/Compiler/DependencyAnalysis/.
• Update ILCompiler.Compiler.csproj and ILCompiler.ReadyToRun.csproj to compile/link the shared file.
• Remove the ReadyToRun-local duplicate interface source entry (and delete the duplicate file).

Reviewed changes

Copilot reviewed 3 out of 4 changed files in this pull request and generated no comments.

File	Description
src/coreclr/tools/Common/Compiler/DependencyAnalysis/IObjectNodeWithAlignment.cs	Adds the shared interface (and XML doc contract) in the common dependency-analysis namespace.
src/coreclr/tools/aot/ILCompiler.ReadyToRun/ILCompiler.ReadyToRun.csproj	Links the shared interface file and removes the ReadyToRun-local compile item.
src/coreclr/tools/aot/ILCompiler.ReadyToRun/Compiler/DependencyAnalysis/ReadyToRun/IObjectNodeWithAlignment.cs	Deletes the ReadyToRun-local duplicate interface definition.
src/coreclr/tools/aot/ILCompiler.Compiler/ILCompiler.Compiler.csproj	Links the shared interface file and removes the project-local compile item.