.Net: [MEVD] Go over all key types, add support for Guid

[roji]

• Added new KeyTypeTests to cover provider key support, alongside the existing DataTypeTests and EmbeddingTypeTests; moved all three into TypeTests folder.
• As discussed offline, this adds Guid-as-string key support for all providers. From research this seems to be very standard practice across a wide range of databases: JSON-based databases generally encode various types (e.g. DateTime) as string, and Guids are standard there. Sqlite is similar, with Microsoft.Data.Sqlite supporting it natively. This notably allows upper layers to assume that they can always use Guid, which helps MEDI (see this issue).
• Per-provider notes
  • Azure AI Search: string only supported, added Guid-as-string as an option (docs encouraging mapping Guid to strings)
  • MongoDB/CosmosMongoDB: Added int and long support (Guid was already supported).
  • CosmosNoSql: Added Guid-as-string (standard practice)
  • Pinecone: Added Guid-as-string
  • Redis: Added Guid-as-string
  • SQL Server: removed DateTime and byte[] as key types (as above) and added Guid.
  • SQLite: The Microsoft.Data.Sqlite (the low-level ADO.NET provider we're built on top of) supports GUIDs as TEXT; so it's really not us deciding to support - it's the lower-level driver. In addition, we support mapping boolean to INTEGER (1/0), which seems similar. Added support as data property as well, not just key.

Closes #11784
Closes #12182

[adamsitnik]

LGTM, but please take a look at my comments as some changes seem to be from a different PR. Thank you @roji for implementing this feature for the Data Ingestion project!