[WIP] Add method extent enumeration support to legacy cDAC

[Copilot]

This change adds the minimal legacy cDAC support needed to expose a method extent through IXCLRDataMethodInstance by implementing StartEnumExtents, EnumExtent, and EndEnumExtents. The implementation is intentionally scoped to the pieces required from the referenced commits and follows the existing enum-handle pattern used by the legacy reader.

• Summary
  • Adds extent enumeration support for legacy method instances so callers can enumerate the method's native code range through the cDAC path.
• What changed
  • Introduces the minimal internal state needed to represent a single method extent and drive the enum lifecycle.
  • Resolves the method extent from runtime metadata, execution-manager state, and GC info.
  • Wires the three new entry points into the legacy ClrDataMethodInstance implementation and preserves debug-time validation against the legacy implementation.

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