[PM-4695] Implement unlock with user key and update examples to use biometrics

[dani-garcia]

- [ ] Bug fix
- [x] New feature development
- [ ] Tech debt (refactoring, code cleanup, dependency upgrades, etc)
- [ ] Build/deploy pipeline (DevOps)
- [ ] Other

Objective

Enable the SDK to export the decrypted user key and expose a way to initialize the SDK with it. The Android and iOS examples have been revamped to allow choosing how to unlock the client.

Some small notes:

• The iOS example is directly storing the user key in a biometric protected keychain, while that doesn't seem possible in Android. Instead, we generate a key in the secure keystore and use it to encrypt/decrypt the user key.
• The iOS example biometrics don't seem to work on the simulator and require a real device for testing.

This depends on the refactor done on #329

[bitwarden-bot]

Checkmarx One – Scan Summary & Details – 596c2166-5695-4a58-b36a-0d5ba8fc4843

New Issues

Severity	Issue	Source File / Package	Checkmarx Insight
	Reflected_XSS	/languages/kotlin/app/src/main/java/com/bitwarden/myapplication/MainActivity.kt: 294	Attack Vector
	Unchecked_Input_for_Loop_Condition	/languages/kotlin/app/src/main/java/com/bitwarden/myapplication/MainActivity.kt: 294	Attack Vector

Fixed Issues

Severity	Issue	Source File / Package
	Reflected_XSS	/languages/kotlin/app/src/main/java/com/bitwarden/myapplication/MainActivity.kt: 115
	Unchecked_Input_for_Loop_Condition	/languages/kotlin/app/src/main/java/com/bitwarden/myapplication/MainActivity.kt: 115

[Hinton]

Looks good, a few minor comments.