FileIndexerConfig::shouldFolderBeIndexe(...) calls folderInList to
determine if the config should be included or excluded.
For a config:
 include: <HOME>/foo
 exclude: <HOME>/foo/bar
the folder "<HOME>/foo/barbaz" would be erroneously excluded, as
folders.startsWith(folder) is true, i.e. the exclude entry would be
used, although folders is the correct match (folders are matched back
This can be avoided by normalizing the config entries to always end
with a trailing slash.
For the config itself this had been handled explicitly, but is no longer
Depends on D18829