Fixes #5840 Custom select folder display breaks after exiting media preview

[LachlanMajor]

When in custom select, if the user long presses an image for a media preview, then exits, the folder display is not the same as it was before the preview. Only the first image is shown and all previously selected images are no longer selected.

Fixes #5840

What changes did you make and why?

ImageFragment.kt:

• notifyDataSetChanged call added after initialisation in handleResult. Now after changes are made, the observers are notified of this change so images are displayed correctly. This fixes the main bug in the issue.
• All code in the passSelectedImages function was removed because they were unnecessary. It would initialise the data set and set the selected images however both of these were called again nearly immediately after, in handleResult, with no changes so passSelectedImages wasn't needed. Function was kept since it was needed for the class, it is just never used.
• setSelectedImages was added to handleResult so previously selected images would be set back to selected after exiting the media preview.

CustomSelectorActivity.kt:

• passSelectedImages call removed in onActivityResult since it is not needed.
• shouldRefresh removed in onActivityResult since that was only for passSelectedImages
• View model's selectedImages value set so selectedImages can be retrieved in handleResult

Tests performed (required)

Tested {build variant} on {Samsung s10 SM-G973F} with API level {31}.

Screenshots (for UI changes only)

Movie001.mp4

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[misaochan]

Thanks @LachlanMajor !