Port documentation improvements from dotnet/runtime#121232

[Copilot]

Ports documentation improvements for ObjectiveCMarshal.CreateReferenceTrackingHandle from dotnet/runtime#121232.

Changes

• Replaced informal Initialize() reference with proper <xref> cross-reference to ObjectiveCMarshal.Initialize* method
• Added explicit "parameter" qualifier to obj parameter mention for clarity

Modified File

xml/System.Runtime.InteropServices.ObjectiveC/ObjectiveCMarshal.xml

- The Initialize() must be called prior to calling this function.
+ The <xref:System.Runtime.InteropServices.ObjectiveC.ObjectiveCMarshal.Initialize*> function must be called prior to calling this function.

- The `obj` must have a type in its hierarchy marked with
+ The `obj` parameter must have a type in its hierarchy marked with

Original prompt

Please create PR that ports changes made in dotnet/runtime#121232 to this repo

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Pull Request Overview

This PR improves the documentation for the ObjectiveCMarshal class by clarifying parameter references and adding proper API cross-references. The changes enhance the readability and consistency of the XML documentation remarks.

• Replaced informal reference "Initialize()" with proper <xref> link to the Initialize method
• Changed "obj" to "obj parameter" for clearer parameter identification