Unify the way for `pdb` to print the stack entry before user input

[gaogaotiantian]

Feature or enhancement

Proposal:

Currently pdb does something like this:

if self.cmdqueue:
    self.cmdqueue.append('w 0')
else:
    self.print_stack_entry(self.stack[self.curindex])

The output is identical in most cases, but there are edges. For example, when display command is involved (which prints stuff in preloop hook). Another inconsistency is about lastcmd - when the user hits enter without any command, the default it to repeat the last command - w 0 could be repeated.

We should make it more consistent so there's only one entry here. It will also lay the foundation in the future where extra information is needed to be printed (e.g. thread/async task info). We don't need to duplicate code in multiple places.

Has this already been discussed elsewhere?

This is a minor feature, which does not need previous discussion elsewhere

Links to previous discussion of this feature:

No response

[gaogaotiantian]

This is done in #120770.