add file line count info on UI (#8396)

Also reworked the header to remove the filename (which is redundant with
the file path above) and made the header a flexbox with a monospace
font.

Fixes: https://github.com/go-gitea/gitea/issues/8170

options/locale/locale_en-US.ini

@@ -681,6 +681,7 @@ stored_lfs = Stored with Git LFS
 commit_graph = Commit Graph
 blame = Blame
 normal_view = Normal View
+lines = lines
 
 editor.new_file = New File
 editor.upload_file = Upload File