[Proposal]: Target-typed generic type inference

# Target-typed generic type inference

* Specification: https://github.com/dotnet/csharplang/blob/main/proposals/target-typed-generic-type-inference.md
* Discussion: https://github.com/dotnet/csharplang/discussions/9628

## Summary
[summary]: #summary

Generic type inference may take a target type into account. For instance, given:

```csharp
public class MyCollection
{
public static MyCollection Create() { ... }
}
public class MyCollection : IEnumerable { ... }
```

We would allow the `Create` method to be called without type argument when it can be inferred from a target type:

```csharp
IEnumerable c = MyCollection.Create(); // 'T' = 'string' inferred from target type
```

## Design meetings

* https://github.com/dotnet/csharplang/blob/main/meetings/2025/LDM-2025-08-18.md#type-inference
* https://github.com/dotnet/csharplang/blob/main/meetings/2025/LDM-2025-08-20.md#target-type-inference-improvements
* https://github.com/dotnet/csharplang/blob/main/meetings/2026/LDM-2026-08-19.md#type-parameter-inference-for-constructor-calls