revert(BitField): ⏪ Bring back-compatibility after BitField serialization

[DraftProducts]

Please describe the changes this PR makes and why it should be merged:

In #4879, some modifications were made to permissions and bitfield methods.
Especially on the type of bitfields that moves from number to BigInt.

This move has some impact on serialization and deserialization.
Take the example of a simple JSON.stringify and JSON.parse.
The method toJSON() (provided by BitField class) will be called and the type (BigInt in the case of Permissions) will be transformed into a string:

8n => "8"

In the past, this type changing was not needed because a number remains a number.
In the actual Bitfield class if you try to pass permissions that went through serialization and deserialization you get the beautiful error BITFIELD_INVALID.
So a simple role or channel creation bring you to a crash of your action.

This PR is here to provide compatibility between Bigint stringified and BitFields.

Status and versioning classification:

• Code changes have been tested against the Discord API, or there are no code changes
• I know how to update typings and have done so, or typings don't need updating

Stale

Stale