Avoids N+1 query when path fileter is triggered

Currently gitaly can return large number of filename search results,
but since binary_path is not set, our ruby filter would acquire it by
fetching blob data from gitaly, causing performance issue.

By setting binary_path, the fetching can be avoided.

changelogs/unreleased/118669-blob-preload.yml

+---
+title: Fix slow query on blob search when doing path filtering
+merge_request: 21996
+author:
+type: performance

lib/gitlab/file_finder.rb

@@ -37,7 +37,7 @@ module Gitlab
 
     def find_by_path(query)
       search_paths(query).map do |path|
-        Gitlab::Search::FoundBlob.new(blob_path: path, project: project, ref: ref, repository: repository)
+        Gitlab::Search::FoundBlob.new(blob_path: path, path: path, project: project, ref: ref, repository: repository)
       end
     end
 

spec/lib/gitlab/file_finder_spec.rb

@@ -30,5 +30,11 @@ describe Gitlab::FileFinder do
 
       expect(results.count).to eq(1)
     end
+
+    it 'does not cause N+1 query' do
+      expect(Gitlab::GitalyClient).to receive(:call).at_most(10).times.and_call_original
+
+      subject.find(': filename:wm.svg')
+    end
   end
 end

spec/lib/gitlab/project_search_results_spec.rb

@@ -86,8 +86,7 @@ describe Gitlab::ProjectSearchResults do
     it "loads all blobs for path matches in single batch" do
       expect(Gitlab::Git::Blob).to receive(:batch).once.and_call_original
 
-      expected = project.repository.search_files_by_name(query, 'master')
-      expect(results.map(&:path)).to include(*expected)
+      results.map(&:data)
     end
 
     it 'finds by content' do