[Feature request] Encrypted ISO boot and validation support

[AniLeo]

Branching off from the original ticket at #4021 for specific follow-ups

For this ticket:

• Once the ISO is detected as being encrypted, we should load .dkey (redump) decryption keys, also provided by the user, and decrypt the ISO contents on-the-fly and boot the game. The ISO should remain encrypted in disk and, ideally, we shouldn't need to write a full temporary decrypted copy of it to disk.
• Implement ISO checksum validation, as we have the database of checksums on redump metadata for encrypted ISO - we could also bundle the checksums as a database with the emulator and periodically update it with new additions.

[matheuswillder]

I like the approach of bundle the checksums as a database in the emulator itself.

For Dolphin, they seems to do this on-the-fly, it can verify the Redump checksum directly from its GUI, but the verification fails if there's no internet connection, so probably they host their checksums database somewhere and the emulator connects to the server to verify if it matches. It's not an approach I particularly like, the emulator connecting to a server for something that could be done locally like this.

[mirh]

Pcsx2 ships it locally, though it becomes its own kind of a thing that you must remember to bump every now and then.

Is solving this 90% of the way there, to straight up boot games from the original game discs?

[digant73]

For the first bullet (encrypted ISO) I would ask @Functionable, could you be available for that task?

For the second bullet (validation), IMO it could be good to follow the same logic currently used for Patches DB and Game Compatibility DB, so to allow the download of the DB (e.g. for any update) and store it locally for the check. Of course a DB provided with the base application is welcome