gh-140131: Fix REPL cursor position on Windows when module completion suggestion line hits console width

[tanloong]

This skips handling the wrapping in self.__write_changed_line() when wlen(newline)==self.width, and simply updates self.posxy (explained in #140131 (comment)).

One thing that happens after the skip is that the cursor moves leftward by one character on Tab key:

WindowsTerminal_eDpHfMhTvA.mp4

As noted in this comment, "when writing to the final character on the line, the cursor location is effectively moved one element backwards." So, we account for this 1-character offset by setting the cursor column to a maximum of self.width-1.

WindowsTerminal_0fSumUhJoh.mp4

• Issue: Import autocomplete in the REPL on Windows moves the text to the end of the next line #140131