Diff stat improvements (#13954)

* Diff stat improvements

- Combine number to just total number of changes
- Add tooltip over stats bar
- Increase contrast on file name
- Refactor classes and CSS to be more reusable

* misc tweaks

* make count bold

options/locale/locale_en-US.ini

@@ -1787,6 +1787,7 @@ diff.whitespace_ignore_all_whitespace = Ignore whitespace when comparing lines
 diff.whitespace_ignore_amount_changes = Ignore changes in amount of whitespace
 diff.whitespace_ignore_at_eol = Ignore changes in whitespace at EOL
 diff.stats_desc = <strong> %d changed files</strong> with <strong>%d additions</strong> and <strong>%d deletions</strong>
+diff.stats_desc_file = %d changes: %d additions and %d deletions
 diff.bin = BIN
 diff.view_file = View File
 diff.file_before = Before