LINQ: Fixes Dictionary.Any() to generate OBJECTTOARRAY SQL (#5595)

The LINQ translator was generating invalid SQL for `Dictionary<string,
object>.Any()` queries. It treated dictionaries as standard enumerables
and used `JOIN` instead of Cosmos DB's required `OBJECTTOARRAY()`
function.

## Root Cause

`TypeSystem.IsEnumerable()` returns true for `Dictionary<K,V>` (via
`IEnumerable<KeyValuePair<K,V>>`), causing `ExpressionToSQL` to
translate dictionary access as a standard collection JOIN operation.

## Changes

- **TypeSystem.cs**: Added `IsDictionary()` check to identify dictionary
types
- **ExpressionToSQL.cs**: Wrap dictionary member access with
`OBJECTTOARRAY()` conversion
- **LinqDictionaryQueryTests.cs**: Added tests for dictionary query
translation

## Example

```csharp
// Query with Dictionary property
var query = container.GetItemLinqQueryable<MyDoc>()
    .Where(d => d.AdditionalData.Any(kvp => kvp.Value == searchFor));
```

**Before (invalid SQL):**
```sql
SELECT * FROM c 
WHERE EXISTS(SELECT VALUE x FROM x IN c.AdditionalData WHERE x.v = @Searchfor)
```

**After (correct SQL):**
```sql
SELECT * FROM c 
WHERE EXISTS(SELECT VALUE x0 FROM x0 IN (SELECT VALUE ObjectToArray(c["AdditionalData"])) 
             WHERE x0["v"] = @Searchfor)
```

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