Group by with DefaultIfEmpty on a sub-query with a left join changes the subquery's joins to inner joins

## File a bug

The projection starts of being correct, but after joining to it using `DefaultIfEmpty()` the resulting query ends up incorrect. This only seems to happen when using `from x in db.xx.Where().DefaultIfEmpty()` syntax to join, `join x in db.xx` version seems okay (see below).

So, this sample code using `Microsoft.EntityFrameworkCore.Sqlite` but this also happens in `Microsoft.EntityFrameworkCore.SqlServer`. I've attached the full project here: [Console3.zip](https://github.com/dotnet/efcore/files/8105996/Console3.zip)

```C#
using Console3;
using Microsoft.EntityFrameworkCore;

using (var db = new BloggingContext())
{
var postCount = db.Posts
.GroupBy(x => x.BlogId, (x, g) => new { BlogId = x, Count = (int?)g.Count() });

var totalCounts =
from b in db.Blogs
from pc1 in postCount.Where(x => x.BlogId == b.BlogId).DefaultIfEmpty()
group new { b.BlogId, pc1.Count } by b.BlogId into g
select new
{
BlogId = g.Key,
Count = g.Sum(x => x.Count)
};

var query =
from b in db.Blogs
from c in totalCounts.Where(x => x.BlogId == b.BlogId).DefaultIfEmpty()
select new
{
b.BlogId,
b.Url,
c.Count
};

Console.WriteLine(totalCounts.ToQueryString());
Console.WriteLine(query.ToQueryString());
}
```

Produces the following output:

```SQL
SELECT "b"."BlogId", COALESCE(SUM("t"."Count"), 0) AS "Count"
FROM "Blogs" AS "b"
LEFT JOIN (
SELECT "p"."BlogId", COUNT(*) AS "Count"
FROM "Posts" AS "p"
GROUP BY "p"."BlogId"
) AS "t" ON "b"."BlogId" = "t"."BlogId"
GROUP BY "b"."BlogId"
```
```SQL
SELECT "b"."BlogId", "b"."Url", "t0"."Count"
FROM "Blogs" AS "b"
LEFT JOIN (
SELECT "b0"."BlogId", COALESCE(SUM("t"."Count"), 0) AS "Count"
FROM "Blogs" AS "b0"
INNER JOIN (
SELECT "p"."BlogId", COUNT(*) AS "Count"
FROM "Posts" AS "p"
GROUP BY "p"."BlogId"
) AS "t" ON "b0"."BlogId" = "t"."BlogId"
GROUP BY "b0"."BlogId"
) AS "t0" ON "b"."BlogId" = "t0"."BlogId"
```

As you can see the inner most join is changed for a left join to an inner join.

I've found that using more traditional join syntax produces the correct SQL. So this works:

```C#
var totalCounts =
from b in db.Blogs
// from pc1 in postCount.Where(x => x.BlogId == b.BlogId).DefaultIfEmpty()
join x in postCount on b.BlogId equals x.BlogId into x
from pc1 in x.DefaultIfEmpty()
group new { b.BlogId, pc1.Count } by b.BlogId into g
select new
{
BlogId = g.Key,
Count = g.Sum(x => x.Count)
};
```

### Include provider and version information

EF Core version: 6.0.2 (and I've confirmed it exists in 6.0.0 and 6.0.1)
Database provider: Microsoft.EntityFrameworkCore.SqlServer
Target framework: .NET 6.0
Operating system: Windows 11
IDE: VSCode 1.64.2