indexing should skip test data directories

[alanz]

Describe the bug

Files in test/xxxx_SUITE_data directory are indexed.

In the case of https://github.com/WhatsApp/erlfmt/tree/master/test/erlfmt_SUITE_data, this has a unicode.erl module which clashes with the system one.

[dgud]

And it don't work :-(
I tested this way to quick it seems, because after the indexing is completely done, files in SUITE_data are still found.

The cause is that els_indexing:index_dir/2 calls els_utils:fold_files/4 which is recursive.

This contradicts the recursive argument in els_config:project_paths which takes an argument recursive which
is false in most cases.

  ok = set(apps_paths     , project_paths(RootPath, AppsDirs, false)),
  ok = set(deps_paths     , project_paths(RootPath, DepsDirs, false)),
  ok = set(include_paths  , include_paths(RootPath, IncludeDirs, false)),
  ok = set(otp_paths      , otp_paths(OtpPath, false) -- ExcludePaths),
  ok = set(lenses         , Lenses),
  ok = set(diagnostics    , Diagnostics),
  %% All (including subdirs) paths used to search files with file:path_open/3
  ok = set( search_paths
          , lists:append([ project_paths(RootPath, AppsDirs, true)
                         , project_paths(RootPath, DepsDirs, true)
                         , include_paths(RootPath, IncludeDirs, false)
                         , otp_paths(OtpPath, true)
                         ])

But that doesn't seem to matter since in the end a recursive search is always used anyway,
at least in all places where els_utils:fold_files/4 is used.

How should we solve this?