[flutter_local_notifications_linux] Add support for the file path icons

[proninyaroslav]

Adding the FilePathLinuxIcon class will allow the developer to specify a custom path in the file system to the icon, if other options, such as AssetsLinuxIcon, aren't suitable (for example, the assets path is different from the standard one).

Close #1565

[MaikuB]

Thanks for updating the PR. Will review and test as soon as I can

[MaikuB]

Thanks. LGTM but as mentioned in #1565, I'd like to see if @dballard could also give this a spin and provide feedback

[dballard]

It appears good to me but I am struggling to test it in our app, I can adjust pubspec.lock to include a path to flutter_local_notifications but not flutter_local_notifications_linux because it's a dep by version of flutter_local_notifications.

But I think I now have code to use it, so if I still have problems I can always try following up with a PR now that the hard work is done! thanks!

[MaikuB]

@dballard thanks for the update. I believe your issue could be solved using https://dart.dev/tools/pub/dependencies#dependency-overrides

[dballard]

thanks @MaikuB that did the trick!
can confirm this works for our use case!
thank you so much @proninyaroslav this is awesome!