crypto.ecdsa: the last bits of migration steps

[blackshirt]

This follow-up PR from the last commited pr. In this PR, its done by migrating the last bits required to be changed, ie .bytes() method on the PrivateKey and PublicKey.
Its was done by using high level function. All info's of EVP_PKEY opaque was already availables on both of them by previous migrations. This series contains the bits forms:

• The changes on .bytes() on the both of PrivateKey and PublicKey
• Adds required definitions
• Some fixs of private and public key loader

After this PR, we can start out to cleanup some deprecated code. Should be this cleanup phase done in gradually step ?

[huly-for-github]

Connected to Huly®: V_0.6-22280

[JalonSolov]

V "policy" is to add @[deprecated] attributes, and set a date for 6 months in the future before the deprecation warning turns into an error.

[blackshirt]

V "policy" is to add @[deprecated] attributes, and set a date for 6 months in the future before the deprecation warning turns into an error

Actually, this series was not about deprecation, .. I think its can be done in the last step after cleans up with the reasons,
The mean with deprecated code was mostly for deprecated EC_KEY functions

[spytheman]

Deprecating public APIs and declarations takes time (to give the users time to update their own code).

Code that is not public, can be just deleted, when it is no longer used.