This PR adds comprehensive XML documentation comments for classes and public/protected/internal methods in the src/Xamarin.Android.Build.Tasks/Utilities/LlvmIrGenerator/ directory.

Summary

Added missing documentation for 20 out of 46 files (43% complete) in the LLVM IR generator, establishing clear documentation patterns and providing substantial coverage of the core infrastructure.

Changes Made

Core Infrastructure Documentation:

• LlvmIrComposer.cs - Abstract base class for composing LLVM IR modules
• LlvmIrVariable.cs - Variable classes, enums, and core variable system (major file)
• LlvmIrVariableOptions.cs - Variable configuration options with predefined option sets
• StringHolder.cs - String management with encoding support and comparison semantics

Enums and Constants:

• LlvmIrLinkage.cs - LLVM linkage types (external, internal, private, etc.)
• LlvmIrStringEncoding.cs - String encoding options (UTF8, Unicode)
• LlvmIrWritability.cs - Variable writability specifications
• LlvmIrAddressSignificance.cs - Address significance options
• LlvmIrIcmpCond.cs - Integer comparison conditions for icmp instructions
• LlvmIrRuntimePreemption.cs - Runtime preemption settings
• LlvmVisibility.cs - Symbol visibility options
• LlvmIrCallMarkers.cs - Call optimization markers (tail, mustTail, noTail)
• LlvmIrKnownMetadata.cs - Well-known LLVM metadata constants
• LlvmIrModuleMergeBehavior.cs - Module merge behavior constants

Attributes and Annotations:

• NativePointerAttribute.cs - Attribute for marking native pointer members
• NativeClassAttribute.cs - Attribute for marking native structure classes
• NativeAssemblerAttribute.cs - Comprehensive assembler generation attributes

Utility Classes:

• TypeUtilities.cs - Type system utilities with extension methods
• MemberInfoUtilities.cs - Member reflection utilities for attribute processing

Documentation Standards

All documentation follows C# XML documentation standards with:

• <summary> tags explaining purpose and usage context
• <param> tags describing parameter purposes and constraints
• <returns> tags explaining return values and possible states
• <exception> tags documenting when exceptions are thrown
• Consistent formatting and meaningful descriptions

Example

/// <summary>
/// Abstract base class for composing LLVM IR modules. Provides a framework for constructing and generating LLVM IR code.
/// </summary>
abstract class LlvmIrComposer
{
    /// <summary>
    /// Generates LLVM IR code for the specified target architecture and writes it to the output stream.
    /// </summary>
    /// <param name="module">The LLVM IR module to generate code from.</param>
    /// <param name="arch">The target Android architecture.</param>
    /// <param name="output">The stream writer to write the generated LLVM IR code to.</param>
    /// <param name="fileName">The name of the file being generated.</param>
    /// <exception cref="InvalidOperationException">Thrown when the module has not been constructed yet.</exception>
    public void Generate(LlvmIrModule module, AndroidTargetArch arch, StreamWriter output, string fileName)

Remaining Work

The following 26 files still need documentation:

• Core framework: LlvmIrGenerator.cs, LlvmIrModule.cs, LlvmIrFunction.cs, LlvmIrInstructions.cs
• Target implementations: LlvmIrModuleTarget.cs and architecture-specific modules
• Data management: String, buffer, and type management classes
• Structure support: StructureInfo.cs, StructureInstance.cs, etc.

This PR establishes clear patterns for completing the remaining documentation.

Addressing #10284.

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