DiscriminatorValue does not support custom values

[IonBazan]

Bug Report

Q	A
BC Break	yes
Version	2.15.1

Summary

Using #[DiscriminatorValue] with custom value does not yield expected results. This was discovered when adding types to ClassMetadata and realized that discriminatorValue and defaultDiscriminatorValue are storing class-string, while discriminatorMap supports any string or int keys.

Current behavior

Following mapping:

#[ODM\MappedSuperclass]
#[ODM\DiscriminatorField('type')]
#[ODM\InheritanceType('SINGLE_COLLECTION')]
class GH2936Superclass
{
    #[ODM\Id]
    public ?string $id;
}

#[ODM\Document]
#[ODM\DiscriminatorValue('foo')]
class GH2936FooDocument extends GH2936Superclass
{
}

Does not allow defining custom values for each document. While #[DiscriminatorValue] accepts a value, it currently has to be the FQCN of the document which defeats the purpose. Custom values can only be defined using #[DiscriminatorMap] at the moment.

How to reproduce

See following failing test: https://github.com/IonBazan/mongodb-odm/blob/test-discriminator-value/tests/Tests/Functional/Ticket/GH2936Test.php

Expected behavior

It should be possible to easily define additional discriminator mapping using child classes' #[DiscriminatorValue] attribute.

See also #644