Use file icons for repository tree rows

app/assets/javascripts/repository/components/table/row.vue

app/assets/javascripts/vue_shared/components/file_icon.vue

app/assets/stylesheets/pages/tree.scss

changelogs/unreleased/ph-treeFileIcons.yml

...epository/components/table/__snapshots__/row_spec.js.snap

spec/frontend/repository/components/table/row_spec.js

spec/frontend/vue_shared/components/file_icon_spec.js