Memory leak when viewing saved form

[seadowg]

Blocked by #5420

ODK Collect version

v2024.3

Problem description

Viewing and then exiting a saved form causes a memory leak as the in memory representation of the form is not cleared away on exit.

Steps to reproduce the problem

1. Finalize a form
2. Open the form in Ready to Send
3. Exit the form

The memory usage of the app will increase each time you repeat 2 and 3 (even after garbage collection).

Expected behavior

The memory increase after viewing a form should be cleaned up by garbage collection.

Other information

This happens because when we open a form to view we start ViewOnlyHierarchyActivity and finish FormFillingActivity immediately without calling exit() which cleans up the form session in FormSessionRepository. This means that the FormController (and other form data) are held in memory indefinitely.

We could potentially fix this easily by just clearing the form session when exiting ViewOnlyHierarchyActivity.