[Android] Fix rewards db import on Android 10

[samartnik]

Description

There is additional security layer on Android 10, that prevents from copying db file directly from Downloads folder. Needs to be fixed.

Steps to reproduce

Actual result

Expected result

Issue reproduces how often

Issue happens on

• Current Play Store version?
• Beta build?

Device details

• Install type (ARM, x86):
• Device (Phone, Tablet, Phablet):
• Android version:

Brave version

Website problems only

• Does the issue resolve itself when disabling Brave Shields?
• Does the issue resolve itself when disabling Brave Rewards?
• Is the issue reproducible on the latest version of Chrome?

Additional information

[samartnik]

Test plan:

1. Try to import database on Android 10;
2. No errors should be shown on that;

[srirambv]

Verification passed on Samsung Tab A with Android 10 running 1.11.100 x64 build

• Verified able to import db without any errors or failure

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Verification passed on OnePlus 6T with Android 10 running 1.11.100 x64 build

• Verified able to import db without any errors or failure