Can't map Dictionary<string,object> (e.g. to JSON) since it's detected as a property bag

With (PostgreSQL) native JSON support, it’s useful to map Dictionary directly to JSON columns. This works e.g. for Dictionary<string,string>, but fails for Dictionary<string,object> since the property is detected as a property bag:

public class Blog
{
    public int Id { get; set; }

    [Column(TypeName = "jsonb")]
    public Dictionary<string, object> JsonProperty { get; set; }
}

The exception:

The navigation 'Blog.JsonProperty' must be configured in 'OnModelCreating' with an explicit name for the target shared-type entity type, or excluded by calling 'EntityTypeBuilder.Ignore'.

We may want to stop detecting property bags if column has an explicit store type. Following on how type converters work, this can be worked around by configuring the property with .Metadata.SetProviderClrType(null).

/cc @AndriySvyryd

Originally filed by @ColinZeb in https://github.com/npgsql/efcore.pg/issues/2134

[AndriySvyryd]

Related to https://github.com/dotnet/efcore/issues/28871

[roji]

@Mfolmer you’re definitely not supposed to be able to map a Dictionary<string, object> via ToJson. At this point, ToJson is only for mapping strongly-typed CLR-based entity types. We have plans to improve on that (#28871), though support is likely to take the form of JsonDocument/JsonElement support rather than via Dictionary.