This change migrates the alias tests (BasicAliasTest and SyncAliasTest)
to JUnit 5. It replaces the usage of the WorkspaceTestRule with the
WorkspaceResetExtension as. The deletion of files and file stores via
the WorkspaceTestRule is replaced with dedicated file delete operations
exactly where they are required. The creation of temporary file stores
is replaced with the usage of temporary directories that are
automatically cleaned up via the according JUnit 5 extension. The
recursive folder deletion implementation from the
SessionCustomizationUtil is used by generalizing it to the
FileSystemHelper class.

Contributes to
https://github.com/eclipse-platform/eclipse.platform/issues/903