[WIP] Fix bug with existing butterfly files directory on Android

[Copilot]

Thanks for assigning this issue to me. I'm starting to work on it and will keep this PR's description up to date as I form a plan and make progress.

Original prompt

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This section details on the original issue you should resolve

<issue_title>[Bug]: use existing directory of butterfly files with another installation</issue_title>
<issue_description>### What happened?

I have directory in ./Documents for Butterfly files, but a can not add it as data folder an Android.
This prevents from using both nightly and stable version on the same device, and also using the app from other device with synced storage.

Version

2.4.1

Platform

Android

Relevant log output

Code of Conduct

• I agree to follow this project's Code of Conduct</issue_description>

Comments on the Issue (you are @copilot in this section)

@CodeDoctorDE Im not sure what you mean. You can change the data directory in the settings @CodeDoctorDE Strange, tested it myself and it works correctly and will be changed successfully. Can you give me more specific information about your device? @CodeDoctorDE Okay... does this also happen in the nightly version? @CodeDoctorDE Can reproduce it, but sadly looks like an android specific permission issue: ``` E/flutter ( 5910): [ERROR:flutter/runtime/dart_vm_initializer.cc(40)] Unhandled Exception: PathAccessException: Cannot copy file to '/storage/emulated/0/Documents/Butterfly/Templates/Light.bfly', path = '/storage/emulated/0/Android/data/dev.linwood.butterfly.nightly/files/Linwood/Butterfly/Templates/Light.bfly' (OS Error: Permission denied, errno = 13) ```

I'm open for ideas/pull requests that fixes the issue.

The problem is this:
I'm using ACTION_OPEN_DOCUMENT_TREE to get the folder with file picker: https://github.com/miguelpruivo/flutter_file_picker.

https://developer.android.com/training/data-storage/shared/documents-files?hl=en#grant-access-directory

https://github.com/miguelpruivo/flutter_file_picker/blob/33476e19bb660c4258e8f4b46b28ddbe7749384b/android/src/main/kotlin/com/mr/flutter/plugin/filepicker/FileUtils.kt#L135</comment_new>

• Fixes [Bug]: use existing directory of butterfly files with another installation #1000

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