Fix dictionary key order sensitivity in Spector tests for languages with non-deterministic ordering

[Copilot]

This PR resolves an issue where Spector tests would fail when client libraries sent JSON dictionaries with keys in different orders than expected, which was particularly problematic for languages like Rust where HashMap key order is not guaranteed.

Problem

When Rust clients (and other languages with non-deterministic object key ordering) sent dictionary data to Spector mock APIs, tests would fail even when the data was semantically identical:

// Rust client sends:
{"k2": 2, "k1": 1}

// Spector expects:
{"k1": 1, "k2": 2}

The raw body validation used strict string comparison, causing these semantically equivalent JSON objects to be treated as different.

Solution

Enhanced the validateRawBodyEquals function in @typespec/spec-api to perform semantic JSON comparison when both the actual and expected bodies are JSON content, while preserving exact string comparison for non-JSON content.

Key Changes

1. Added JSON detection: isJsonContent() helper safely identifies JSON strings
2. Semantic JSON comparison: Parse and compare JSON objects semantically for key order independence
3. Graceful fallback: Falls back to string comparison if JSON parsing fails
4. Preserved behavior: Non-JSON content (plain text, binary) still uses exact comparison

Example

// Before: This would fail ❌
validateRawBodyEquals(
  { rawBody: '{"k2":2,"k1":1}' },
  '{"k1":1,"k2":2}'
);

// After: This now passes ✅
validateRawBodyEquals(
  { rawBody: '{"k2":2,"k1":1}' },
  '{"k1":1,"k2":2}'
);

Testing

• ✅ All existing tests continue to pass
• ✅ Added comprehensive test suite covering dictionary ordering scenarios
• ✅ Verified edge cases (invalid JSON, non-JSON content, semantic differences)
• ✅ Manual testing confirms fix works for real-world TypeSpec dictionary patterns

Impact

• Rust clients: Can now use HashMap without worrying about serialization key order
• Other languages: Any language with non-deterministic object key order now works
• Backward compatibility: Zero impact on existing functionality
• Performance: Minimal overhead - only parses JSON when both sides are JSON-like

Fixes #7687.

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