Fix for missing paths in simple suffix evaluation

Summary:
# Bug Description
Watchman would return with missing path components
S468253

# This Diff
Adds the relative root into the path evaluation

# Technical Details
Previously without this change, the contents of the EdenFileResult would be missing the relative root component, causing following path evaluators to remove the same number of paths from the head of the desired path

Reviewed By: ezzak

Differential Revision: D65901018

fbshipit-source-id: b47700a3802a23f59af2b7da7f172f8e0caf631b

Author: Chris Dinh

watchman/watcher/eden.cpp

@@ -903,7 +903,7 @@ class EdenView final : public QueryableView {
       auto file = make_unique<EdenFileResult>(
           rootPath_,
           thriftChannel_,
-          w_string::pathCat({mountPoint_, item.name}),
+          w_string::pathCat({mountPoint_, relative_root, item.name}),
           /*ticks=*/nullptr,
           /*isNew=*/false,
           item.dtype);