Add support for IStringLocalizerFactory and IStringLocalizer to allow for as many localizers as needed.

[npavlyk82]

We need to get translations from different sources, such as JSON files, databases, etc.

The current logic has the following limitations:

1. It doesn't allow for the use of multiple implementations of the IResourcesProvider interface and choosing the appropriate one depending on the path.
2. IResourcesProvider::TryGetResourceAsync supports only complex keys, which is a blocker for implementing some composite type for IResourcesProvider.

3. IResourcesProvider is always registered in DI with a Singleton lifetime.

I would implement a solution using existing interfaces from the Microsoft.Extensions.Localization package. The current logic can be extended without breaking existing functionality.