vi mode: `d` deletes something other than the selected characters (block select)

Hi, thanks for this library, it's handy.

I have written three tests to demonstrate this bug

1. test_vi_delblock passes. This test runs vi to check my assumption that d should indeed delete a block selection.
2. test_example_delblock fails. This is the problematic behavior. If you select the first character of all three lines and press d, you should still have the remaining characters on all three lines. Instead you lose every character on the first two lines, and the last line remains untouched
3. test_example_cutblock passes. This shows prompt toolkit doing the right thing and deleting only the first character on each line. However, it should do this for both x and d, not just for x

import pexpect
import pyte, os
from textwrap import dedent

ROWS, COLS = 15, 40
screen = pyte.Screen(COLS, ROWS)
stream = pyte.Stream(screen)

def spawn_process(cmd):
    env = os.environ.copy()
    env.update({'LINES': str(ROWS), 'COLUMNS': str(COLS)})
    return pexpect.spawn(cmd, echo=False, encoding='utf-8', dimensions=(ROWS, COLS), env=env)

def emulate_ansi_terminal(raw_output):
    stream.feed(raw_output)
    lines = screen.display
    screen.reset()
    return '\n'.join(lines)

def test_vi_delblock():
    "you can use 'd' to delete a block selection in vi"

    p = spawn_process('vi')
    p.send("iabc\ndef\nghi")        # some text to edit
    p.sendcontrol("[")              # press esc
    p.send("0")                     # beginning of line
    p.sendcontrol("v")              # block select
    p.send("kkd")                   # this and two lines above, then delete
    p.expect(pexpect.TIMEOUT, timeout=2)
    output = emulate_ansi_terminal(p.before)
    print(output)
    assert '\n'.join(output.split()[0:3]) == dedent(
        """
        bc
        ef
        hi
        """
    ).strip()

def test_example_delblock():
    "but prompt toolkit ignores the block select when 'd' is pressed"

    p = spawn_process('sh -c "python $HOME/src/python-prompt-toolkit/examples/prompts/switch-between-vi-emacs.py"')
    p.send("abc\ndef\nghi")             # type something
    p.send(chr(27) + chr(79) + chr(83)) # switch to vi mode (F4, accoring to https://stackoverflow.com/a/73355658/1054322)
    p.sendcontrol("[")                  # press esc
    p.send("0")                         # beginning of line
    p.sendcontrol("v")                  # block select
    p.send("kkd")                       # this and two lines above, then delete
    p.expect(pexpect.TIMEOUT, timeout=2)
    output = emulate_ansi_terminal(p.before)
    print(output)

    # lines 1 & 2 say: WARNING: your terminal doesn't support cursor position requests (CPR)
    assert '\n'.join(map(lambda x: x.strip(), output.split("\n")[2:5])) == dedent(
        """
        > bc
        ef
        hi
        """
    ).strip()
    # fails, instead output has:

    #
    #
    # ghi

    # which is *almost* what would have happened if this had been `v` instead of `ctrl + v`

def test_example_cutblock():
    "you do, however, get the desired behavior for 'd' if you use 'x' instead"

    p = spawn_process('sh -c "python $HOME/src/python-prompt-toolkit/examples/prompts/switch-between-vi-emacs.py"')
    p.send("abc\ndef\nghi")             # type something
    p.send(chr(27) + chr(79) + chr(83)) # switch to vi mode (F4, accoring to https://stackoverflow.com/a/73355658/1054322)
    p.sendcontrol("[")                  # press esc
    p.send("0")                         # beginning of line
    p.sendcontrol("v")                  # block select
    p.send("kkx")                       # this and two lines above, then cut
    p.expect(pexpect.TIMEOUT, timeout=2)
    output = emulate_ansi_terminal(p.before)
    print(output)
    assert '\n'.join(map(lambda x: x.strip(), output.split("\n")[2:5])) == dedent(
        """
        > bc
        ef
        hi
        """
    ).strip()

Start by running the reported test_example_delblock scenario against examples/prompts/switch-between-vi-emacs.py, then compare it with test_example_cutblock and test_vi_delblock. Trace the vi block-selection handling for d and x; done means d leaves bc, ef, and hi, matching the block behavior demonstrated by x.