feat: Implement ActivityResultContract

[stefan-niedermann]

Motivation:

• Provide state-of-the-art access to Nextcloud Single Sign On
• Hide complete permission granting and account importing process behind a clear API surface
• Deprecate methods that rely on deprecated Android framework methods like onActivityResult
• Enhance maintainability and make refactoring easier in the future when the deprecated methods have eventually been removed or marked as private

Refs: #448

Co-authored-by: Gemini

🤖 AI (if applicable)

• The content of this PR was partly or fully generated using AI

[codacy-production]

Not up to standards ⛔

🔴 Issues 2 high · 1 minor

Alerts:
⚠ 3 issues (≤ 0 issues of at least minor severity)

Results:
3 new issues

Category	Results
ErrorProne	2 high
CodeStyle	1 minor

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🟢 Metrics 16 complexity

Metric	Results
Complexity	16

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[stefan-niedermann]

Additional information

Exception Handling

A third party app can start the import process and gets either a SingleSignOnAccount instance or null. Displaying errors to the users is handled intentionally completely within the SSO lib.

This aligns with other ActivityResultContracts and gives the SSO lib the full control over exception handling for a uniform user experience across various 3rd party apps.

Theming

There are multiple sources of dialogs that may look different within the flow:

• Native android dialogs like the account chooser
• Permission dialogs from the files app
• Exception dialogs from the SSO lib

Given this does not affect the (now) deprecated way of importing accounts, this can be enhanced progressively in my opinion, so this should not be a show stopper.
Maybe @AndyScherzinger has some ideas how to unify the styling in the complete flow?

Testing

Tested successfully manually on AVD API level 24 without Google Play Services and API Level 36.1 with Google Play Services.

[github-actions]

SpotBugs

Category	Base	New
Bad practice	9	9
Correctness	24	24
Dodgy code	13	16
Internationalization	2	2
Malicious code vulnerability	11	11
Multithreaded correctness	4	4
Performance	4	4
Security	7	7
Total	74	77

SpotBugs increased!