Don't identify dictionary indexer as NRT

[roji]

We currently don't calculate nullability for generic properties, since that's a complex task (dotnet/runtime#29723 is supposed to add this capability to the reflection API at some point). This interferes with the ability to use Dictionary for property bag, since it's a generic type and its indexer is incorrectly identified as non-nullable (the actual nullability of the generic type argument isn't taken into account).

The general inability to handle generic properties hasn't proved problematic - it's been this way since EF Core 3.0 and we've received no user complaints. This is a specific fix to recognize the indexer on Dictionary and not identify it as non-nullable. If this is OK to merge, I'll document the general limitation in our doc page on nullability, and open a separate issue for handling generic properties.

Fixes #20718

[smitpatel]

System.AggregateException : One or more errors occurred. (Introducing FOREIGN KEY constraint 'FK_JoinTwoSelfShared_EntityTwos_RightId' on table 'JoinTwoSelfShared' may cause cycles or multiple cascade paths. Specify ON DELETE NO ACTION or ON UPDATE NO ACTION, or modify other FOREIGN KEY constraints.\r\nCould not create constraint or index. See previous errors.) (The following constructor parameters did not have matching fixture data: ManyToManyLoadSqlServerFixture fixture)\r\n---- Microsoft.Data.SqlClient.SqlException : Introducing FOREIGN KEY constraint 'FK_JoinTwoSelfShared_EntityTwos_RightId' on table 'JoinTwoSelfShared' may cause cycles or multiple cascade paths. Specify ON DELETE NO ACTION or ON UPDATE NO ACTION, or modify other FOREIGN KEY constraints.\r\nCould not create constraint or index. See previous errors.\r\n---- The following constructor parameters did not have matching fixture data: ManyToManyLoadSqlServerFixture fixture

@AndriySvyryd - Shouldn't the convention take care of this?

[AndriySvyryd]

Yes, it should. It might be missing a trigger

[smitpatel]

Approving Andriy's changes

[roji]

Thanks @AndriySvyryd and @smitpatel