If you have added the Microsoft Productivity Power tools extension (which if you haven’t I would recommned) it adds an option to tabify files. This does not apply across all files in a solution, but it’s prompted for when editing each file, on a per file basis. Not quite what you’re after but a help.
Also you might try setting your IDE editor settings to use tabs, then do menu-edit-advanced-format document (CTRL+E,D). This will replace groups of tab length spaces with a tab, and that should be scriptable for all files in the solution via a macro.