Microsoft.Extensions APIs implemented in aspnetcore, but documented in dotnet-api-docs missing documentation

I noticed this as part of #120483

Let this issue track the following:
| Namespace | APIs | Issue |
|-----------|------|-------|
| Microsoft.Extensions.Caching.SqlServer | 6 | #120484 |
| Microsoft.Extensions.Caching.StackExchangeRedis | 9 | #120485 |
| Microsoft.Extensions.DependencyInjection | 3 | #120486 |
| Microsoft.Extensions.Diagnostics.HealthChecks | 3 | #120487 |
| Microsoft.Extensions.Localization | 1 | #120488 |
| Microsoft.Extensions.Logging | 2 | #120490 |
| Microsoft.Extensions.Logging.AzureAppServices | 9 | #120489 |
| Microsoft.Extensions.ObjectPool | 11 | #120491 |
| Microsoft.Extensions.Validation | 41 | #120492 |
| Microsoft.Extensions.WebEncoders | 1 | #120494 |
| Microsoft.Extensions.WebEncoders.Testing | 3 | #120493 |

**Total APIs to document: 89**
**Total namespaces: 11**

These APIs are not built as part of dotent/runtime, so it's not clear to me that they belong in https://github.com/dotnet/dotnet-api-docs. I think other assemblies built from aspnetcore go in https://github.com/dotnet/AspNetApiDocs