[APIView][.NET] Enable Cross-Language Support for C#

Enable cross-language linking for C# packages in APIView, allowing users to view the same API across Python, JavaScript, Java, and C# side-by-side.

## What Needs Fixing

Two changes required:

### 1. Emitter Fix (azure-sdk-for-net repo)

**Location:** `eng/packages/http-client-csharp/emitter/src/emitter.ts`

**Problem:** `generateMetadataFile()` only writes API version, not cross-language mappings.

**Current:**
```json
{ "apiVersion": "2024-05-01" }
```

**Required:**
```json
{
"apiVersion": "2024-05-01",
"crossLanguageDefinitions": {
"CrossLanguagePackageId": "ContentSafety",
"CrossLanguageDefinitionId": {
"Azure.ContentSafety.ContentSafetyClient": "ContentSafety.ContentSafetyClient"
}
}
}
```

**Note:** Infrastructure already exists! `ManagementInputLibrary.cs` has `ModelsByCrossLanguageDefinitionId` - just needs to write it to file.

### 2. Parser Fix
**Location:** `tools/apiview/parsers/csharp-api-parser/`

**Problem:** Parser doesn't read metadata or set `CrossLanguageId`.

**Fix:**
- Accept optional metadata file path argument
- Load and parse the metadata JSON
- Set `CrossLanguageId` on ReviewLines when LineId matches mapping
- Set `CrossLanguageMetadata` on CodeFile

---

## Expected Output

```json
{
"PackageName": "Azure.ContentSafety",
"Language": "C#",
"CrossLanguageMetadata": {
"CrossLanguagePackageId": "ContentSafety",
"CrossLanguageDefinitionId": {
"Azure.ContentSafety.ContentSafetyClient": "ContentSafety.ContentSafetyClient"
}
},
"ReviewLines": [
{
"LineId": "Azure.ContentSafety.ContentSafetyClient",
"CrossLanguageId": "ContentSafety.ContentSafetyClient"
}
]
}
```

---

[C# Cross-Language: Implementation Guide](https://gist.github.com/AlitzelMendez/61c83dd7db205ef66a9ea85ad28bf9fe#file-csharp-md)

Start with eng/packages/http-client-csharp/emitter/src/emitter.ts and the existing ModelsByCrossLanguageDefinitionId data in ManagementInputLibrary.cs, then inspect tools/apiview/parsers/csharp-api-parser/. Verify how the parser receives arguments and represents ReviewLines and CodeFile. Done means metadata is emitted, parsed, and reflected in CrossLanguageMetadata and matching CrossLanguageId values like those in the expected output.

Written by the indexing model from the issue text.