Duplicated prefs in browser.storage.local

NOTE

That fix has to be done as bugfix release for 0.6.1. So Thomas can pick it for 3.15 release ( happening end of October) cc. @d.rebeschini @jensroesler.

Description:

In FF incognito mode, when upgrading from 3.12 (pre webext) to 3.14(EWE 0.4.0) to 3.15 (EWE 0.6.0) filters are "lost" for user. While in the browser.storage.local they are duplicated (file:patterns.ini and abp:file:patterns.ini` are present)

Possible fix:

Migrate all user data again from abp:file:patterns.ini or file:patterns.ini to ewe:file:patterns.ini if there is one of them modified (second will be default/unmodified prefs which means that user didn't change anything).

In case there are both prefs -> select newest one.

@ThomasGreiner does that makes sense and would this idea work?

More context where this bug originates form:

This ticket was created based on the discussions happening on: https://gitlab.com/adblockinc/ext/adblockplus/adblockplusui/-/issues/1247#note_1120412223

Changes in code that caused this situation:

• https://gitlab.com/eyeo/adblockplus/abc/webext-sdk/-/commit/a04ea78619b96e873f294406eebfc7ec88acfc76 upgraded key prefixes in webext-sdk
• https://gitlab.com/eyeo/adblockplus/abc/webext-sdk/-/issues/231 FF incognito mode bug