RedisCacheOptions to Manually Set ConnectionMultiplexer

[NapalmCodes]

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PR Title
RedisCacheOptions to Manually Set ConnectionMultiplexer

PR Description
Adding a Factory Func to allow manual setting of the ConnectionMultiplexer for Redis.
Implemented for both Async and Sync method paths.

Addresses #28379

[dnfadmin]

All CLA requirements met.

[pranavkm]

Should this be nullable?

[pranavkm]

Suggested change

	public Func<IConnectionMultiplexer> ConnectionMultiplexerFactory { get; set; }
	[DisallowNull]
	public Func<Task<IConnectionMultiplexer>>? ConnectionMultiplexerFactory { get; set; }

[NapalmCodes]

What is making this a Task return type buying us exactly?

[pranavkm]

@davidfowl mentioned creating the connection involved I/O. This was meant to reflect that.

[JunTaoLuo]

The Func will likely include an async call e.g. ConnectionMultiplexer.ConnectAsync and this way, the Func can be awaited in other components to get the same connection.

[NapalmCodes]

@JunTaoLuo and @pranavkm I am having some issues with this. Nullable annotations does not appear to be enabled in this class yet:

/Users/dev-spv/aspnetcore/src/Caching/StackExchangeRedis/src/RedisCacheOptions.cs(32,65): error CS8632: The annotation for nullable reference types should only be used in code within a '#nullable' annotations context. [/Users/dev-spv/aspnetcore/src/Caching/StackExchangeRedis/src/Microsoft.Extensions.Caching.StackExchangeRedis.csproj]

I am willing to add these annotations if desired, but I had a ton of issues trying to satisfy the Roslyn Unshipped API file changes with VSCode. Specifically it would not recognize the get as public even though it recognized it was part of the API. Below is what I could not get working in the unshipped text file even when I did have #nullable enabled at the top of the class:

Microsoft.Extensions.Caching.StackExchangeRedis.RedisCacheOptions.ConnectionMultiplexerFactory.get -> System.Func<System.Threading.Tasks.Task<StackExchange.Redis.IConnectionMultiplexer>>? Microsoft.Extensions.Caching.StackExchangeRedis.RedisCacheOptions.ConnectionMultiplexerFactory.set -> void

[JunTaoLuo]

I'll take a look.

[JunTaoLuo]

Let's continue the conversation at #32266