Add R2RDump support for Mach-O composite R2R images

[elinor-fung]

Update R2RDump / ILCompiler.Reflection.ReadyToRun to handle Mach-O composite R2R images

• Make ReadyToRunReady stop operating on PEReader directly
• Add a IBinaryImageReader interface to handle reading of different R2R image types - implementations for PE and MachO
• Move common types and functionality related to Mach-O from Microsoft.NET.HostModel to shared location src/coreclr/tools/Common

[Copilot]

Pull Request Overview

This PR adds support for Mach-O composite ReadyToRun (R2R) images to the R2RDump tool and ILCompiler.Reflection.ReadyToRun library. The implementation introduces an abstraction layer for binary image reading to handle both PE and Mach-O formats uniformly.

Key Changes:

• Introduced IBinaryImageReader interface to abstract binary image reading across PE and Mach-O formats
• Implemented PEImageReader and MachOImageReader as format-specific readers
• Moved common Mach-O types from Microsoft.NET.HostModel to shared location src/coreclr/tools/Common/MachO with conditional compilation for namespace selection

Reviewed Changes

Copilot reviewed 23 out of 23 changed files in this pull request and generated 7 comments.

Show a summary per file

File	Description
IBinaryImageReader.cs	New interface abstracting binary image operations across formats
PEImageReader.cs	PE-specific implementation wrapping PEReader
MachOImageReader.cs	New Mach-O image reader with symbol table parsing and segment resolution
ReadyToRunReader.cs	Refactored to use IBinaryImageReader interface instead of directly using PEReader
ManifestAssemblyMetadata.cs	Added parameterless constructor for Mach-O support where PEReader is unavailable
ReadyToRunMethod.cs	Added debug assertion for PE-specific operations
R2RDiff.cs	Updated to use abstracted GetSections method
NList64.cs	New Mach-O symbol table entry structure
NameBuffer.cs	Added GetString method for reading segment/section names
Segment64LoadCommand.cs	Added GetVMAddress accessor
Section64LoadCommand.cs	Added SectionName, GetVMAddress, and GetSize accessors
MachHeader.cs	Added CpuType accessor
MachObjectFile.cs	Moved IsMachOImage method to shared location with conditional namespaces
Common MachO enums/types	Added conditional compilation for dual namespace support
Project files	Updated to include shared MachO sources

Comments suppressed due to low confidence (1)

src/coreclr/tools/Common/MachO/BinaryFormat/NameBuffer.cs:57

• The GetString() method may not respect byte order. When the struct is created, _nameLower and _nameUpper may be swapped based on endianness (lines 29-38), but GetString() always reads bytes starting from _nameLower. On big-endian systems, the bytes should be read starting from _nameUpper instead. Consider adjusting the implementation to account for endianness similar to how the constructor does.

[davidwrighton]

@adamperlin You should be aware of this effort.