You open Total Commander in that folder, press Alt+F7, put your string into the lower search box and press search. It will give you the list of matching files, with F3 available for quick preview; then you right click the file you need and choose "Open with VS Code" from the context menu.

Sadly, you don't get the "context" (the content of actual matches) out of the box, you'll have to resort to double-tapping F3 while manually going down the file list. That's a downside, I fully admit that.