Analyzer warning and quick fix for ToDictionary over GroupBy

[roji]

We've had discussions in #16730 and offline about the following:

var test = await this.dbcontext.MyEntity
        .GroupBy(x => x.Status)
        .ToDictionary(x => x.Key.Name, y => y.Count());

There is evidence to support that a common expectation is for this to get translated for server evaluation. However, since ToDictionary() is only defined over IEnumerable, EF Core cannot see the aggregate function and the grouping will in fact be performed client-side.

We can have an analyzer to detect this, and even suggest a quick fix of extracting the aggregate lambda inserting a Select() with it between the GroupBy and ToDictionary.

[divega]

The analyzer should probably recognize ToLookup as well.

[molinch]

I would love to see such an analyzer, we just fell into this trap and it was a pain to diagnose. Especially for ToDictionaryAsync since it comes from EF.Core.

[roji]

Reopening to reconsider doing this, now that we're starting to have static analysis capabilities for EF LINQ queries (via precompiled queries).