fix(core): update to TypeScript 4.8 and improve EntityDTO type

[B4nan]

Due to changes in TS 4.8 we had to simplify the AnyEntity type, it no longer contains the __helper and __meta properties. Those are considered internal, and they are in fact still present, just not on the type level. Most places now use just object instead of AnyEntity for the type signatures (e.g. em.find<T extends object>()).

Another semi type level breaking change is the return type of toJSON/toObject/toPOJO, which now uses EntityDTO<this> and respects the populate hints (Loaded type) too, narrowing relations to their PK if they are not populated.

Closes #3417
Closes #2414

[AdriVanHoudt]

I've just hit this error with 4.8 (4.8.0-beta) by doing

import { MikroORM } from "@mikro-orm/core"; // both version 5.3.1
import { PostgreSqlDriver } from "@mikro-orm/postgresql";

MikroORM.init<PostgreSqlDriver>();

index.ts:4:15 - error TS2344: Type 'PostgreSqlDriver' does not satisfy the constraint 'IDatabaseDriver<Connection>'.
  The types returned by 'connect()' are incompatible between these types.
    Type 'Promise<PostgreSqlConnection>' is not assignable to type 'Promise<Connection>'.
      Type 'PostgreSqlConnection' is not assignable to type 'Connection'.
        The types of 'platform.getSchemaGenerator' are incompatible between these types.
          Type '(driver: IDatabaseDriver<Connection>, em?: SqlEntityManager<AbstractSqlDriver<AbstractSqlConnection>> | undefined) => SchemaGenerator' is not assignable to type '(driver: IDatabaseDriver<Connection>, em?: EntityManager<IDatabaseDriver<Connection>> | undefined) => ISchemaGenerator'.
            Types of parameters 'em' and 'em' are incompatible.
              Type 'EntityManager<IDatabaseDriver<Connection>> | undefined' is not assignable to type 'SqlEntityManager<AbstractSqlDriver<AbstractSqlConnection>> | undefined'.
                Type 'EntityManager<IDatabaseDriver<Connection>>' is missing the following properties from type 'SqlEntityManager<AbstractSqlDriver<AbstractSqlConnection>>': createQueryBuilder, qb, raw, getKnex, execute

4 MikroORM.init<PostgreSqlDriver>();
                ~~~~~~~~~~~~~~~~


Found 1 error in index.ts:4

Will this update fix this issue?

[B4nan]

Yes, but I am not interested in doing those changes before stable 4.8 is out, they might fix some things before that happens. Right now TS 4.8 requires quite a huge refactoring as you can see in this PR (and the PR is not complete).

[AdriVanHoudt]

Nice!
Given their release timeline I don't suspect a lot will change until release microsoft/TypeScript#49074