Introduce ExposeKeyedServiceAttribute.

[maliming]

Resolves #18794

---

ExposeKeyedService Attribute

ExposeKeyedServiceAttribute is used to control which keyed services are provided by the related class. Example:

[ExposeKeyedService<ITaxCalculator>("taxCalculator")]
[ExposeKeyedService<ICalculator>("calculator")]
public class TaxCalculator: ICalculator, ITaxCalculator, ICanCalculate, ITransientDependency
{
}

TaxCalculator class exposes ITaxCalculator interface with the key tax and ICalculator interface with the key calculator. That means you can get keyed services from the IServiceProvider as shown below:

var taxCalculator = ServiceProvider.GetRequiredKeyedService<ITaxCalculator>("taxCalculator");
var calculator = ServiceProvider.GetRequiredKeyedService<ICalculator>("calculator");

Notice that the ExposeKeyedServiceAttribute is only expose keyed services. So, you can not inject ITaxCalculator or ICalculator in your application. If you want to expose both keyed and non-keyed services, you can use ExposeServicesAttribute and ExposeKeyedServiceAttribute together as shown below:

[ExposeKeyedService<ITaxCalculator>("taxCalculator")]
[ExposeKeyedService<ICalculator>("calculator")]
[ExposeServices(typeof(ITaxCalculator), typeof(ICalculator))]
public class TaxCalculator: ICalculator, ITaxCalculator, ICanCalculate, ITransientDependency
{
}

This is a small breaking change because IOnServiceExposingContext has changed.

[codecov]

Codecov Report

Attention: 11 lines in your changes are missing coverage. Please review.

Comparison is base (98c5dec) 51.61% compared to head (2218e9d) 51.61%.
Report is 484 commits behind head on dev.

❗ Current head 2218e9d differs from pull request most recent head 0e0c461. Consider uploading reports for the commit 0e0c461 to get more accurate results

Files	Patch %	Lines
...bp/DependencyInjection/OnServiceExposingContext.cs	33.33%	4 Missing ⚠️
...p/DependencyInjection/ConventionalRegistrarBase.cs	91.42%	3 Missing ⚠️
...DependencyInjection/ExposeKeyedServiceAttribute.cs	72.72%	2 Missing and 1 partial ⚠️
...ependencyInjection/DefaultConventionalRegistrar.cs	88.88%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##              dev   #18819    +/-   ##
========================================
  Coverage   51.61%   51.61%            
========================================
  Files        3077     3083     +6     
  Lines       97266    97789   +523     
  Branches     7745     7806    +61     
========================================
+ Hits        50202    50476   +274     
- Misses      45521    45761   +240     
- Partials     1543     1552     +9     

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