We supported multi-line input in pdb in 3.13, but the tab indentation does not work in its best shape. It inserts a\t character, which means the first<tab> will introduce a 2-space (at least looks like it) indentation, and the next ones will introduce a 8-space one.

This PR made it a bit smarter. Now a<tab> at the beginning of the line (before any non-space text) will auto-fill a 4-space indentation. For example,\t and \t will both create a 4-space indentation.

This is not the smartest feature, it's not as good as pyrepl where the indentation is inserted when a new line is created. However, I think it's much better than what we have now.

The ultimate goal is to use pyrepl for pdb, so I don't think duplication too much code to make pdb work slightly better now is that rewarding.

• Issue:Use 4 spaces for indentation in PDB #125377