Check out Mark's good answer as well. There have been some updates to VS Code he mentions that should be considered as well.
Using Shift+Alt+I, you need to cut the text in multiple cursor mode as well:
1Enter2Enter3EnterEnteraEnterbEnterc
Shift+↑↑
Shift+Alt+I
Shift+←
Ctrl+X
↑↑↑↑→
,?
Ctrl+V
As of the 1.23.1 April update, a more convenient, middle mouse button selection can be used.
With the cursor and keyboard,
Instead of cutting the lines like normal, select from the end of the cursor to the beginning while in multi-cursor mode while holding Ctrl+Shift. After cutting the text with Ctrl+X, select with multiple cursors again by holding Ctrl+Shift. Then, type ,? and paste with Ctrl+V like you described.
You can also use Ctrl+Alt+Shift and the direction arrows to select with multiple cursors,
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