Refactoring search logic to use kotlin flows efficiently

[rapterjet2004]

Followup to #5630 , see #5630 (review)

Using the recommended functional programming approach to combining and transforming flows efficiently in the conversation list view model, with new functions added to the data layer to expose the API through a flow, rather than a suspend function, which also simplifies the conversation list activity.

Todo

• Figure out why the adapter is not filtering the regular conversation items correctly.
• Now refreshing the adapter, shows the last filtered search
• Fix tests and suppress codacity linter

🏁 Checklist

• ⛑️ Tests (unit and/or integration) are included or not needed
• 🔖 Capability is checked or not needed
• 🔙 Backport requests are created or not needed: /backport to stable-xx.x
• 📅 Milestone is set
• 🌸 PR title is meaningful (if it should be in the changelog: is it meaningful to users?)

[github-actions]

APK file: https://www.kaminsky.me/nc-dev/android-artifacts/5655.apk



To test this change/fix you can simply download above APK file and install and test it in parallel to your existing Nextcloud app.

[github-actions]

Codacy

Lint

Type	master	PR
Warnings	99	99
Errors	0	0

SpotBugs

Category	Base	New
Bad practice	6	6
Correctness	10	10
Dodgy code	54	54
Internationalization	3	3
Malicious code vulnerability	3	3
Performance	4	4
Security	1	1
Total	81	81