Bug: Paths for Synced Realms appear broken

[cmelchior]

While writing tests for SyncConfiguration.with I noticed that Sync paths appear broken in surprising ways.

It probably happened when we moved support for name() and directory() to Configuration so it is now shared between synced and normal Realms.

[cmelchior]

This probably pulls in #412 as well

[cmelchior]

Intended semantics:

• Synced Realms should be placed in <syncRoot>/<appId>/<userId>/<filename>. The filename is based on the partition value for partition based sync. It will be default.realm for Flexible Sync.
• Setting AppConfiguration.syncRootDirectory will the <syncRoot> to whatever is provided
• Setting SyncConfiguration.directory() will replace the <syncRoot>/<appId>/<userId>/ part.
• Setting SyncConfiguration.name() will replace the <filename>

realm_sync_client_config_set_base_file_path should set the syncRoot
realm_app_sync_client_get_default_file_path_for_realm should create the entire path including the realm file name.

Given that there are various ways we can customize the path, we need to split the path returned from realm_app_sync_client_get_default_file_path_for_realm. This could be done using SystemUtils.PATH_SEPERATOR

[cmelchior]

I do remember some issues with Core setting the root dir name, so if we set the syncroot to /app/files/mongodb-realm/......the path ends up being /app/files/mongodb-realm/mongodb-realm/....

[cmelchior]

After discussing, we don't see a use case for having directory for SyncConfigurations. So we should move directory() so it only exists on RealmConfiguration.