Fix: Save all option overrides attachment files

[mohitsatr]

Fixes #10965

Changes:

1. Makes use of OpenDocumentTree Contract for onSaveAllAttachments option to let users choose a destination folder for all the attachments. Previously, we were forced to click 'save' for each attachment file.
2. Convert AttachmentController.java to Kotlin to make use of Coroutines.

Behaviour:

Screen_Recording_20260506_085902_Thunderbird.Debug.mp4

[github-actions]

✅ Validation Passed: All report and feature-flag labels are correctly set.

[dani-zilla]

This class is one we're planning on deprecating. I understand this was a kotlin conversion of a Java class, but if we're introducing new code (and a small change at that) we should use the newer class. It's net.thunderbird.core.logging.Logger. You can inject an instance of it.

We have more details of it here: https://github.com/thunderbird/thunderbird-android/blob/49e1eab7e2df55ac83ec02e6e3f8c370ac4843c1/core/logging/README.md

[rafaeltonholo]

Although we are aiming to migrate all Java to Kotlin, the conversion should not be done in bug fixes like this one. Having a Kotlin conversion in the same changeset as a bug fix makes it harder to review and to revert in case of necessity. Please, revert the AttachmentController Kotlin conversion and apply the fix on the Java side.

[mohitsatr]

@rafaeltonholo
I'm not familiar with AyncTasks.
Would it be okay if I send a separate PR for AttachmentController.java -> .kt conversion first, and then continue on this PR?

[rafaeltonholo]

@rafaeltonholo I'm not familiar with AyncTasks. Would it be okay if I send a separate PR for AttachmentController.java -> .kt conversion first, and then continue on this PR?

Yes, please! Here is the GitHub issue for the conversion: #11096