Readline vi-mode doesn't work as expected

Problem overview

The new irb version appears to have problems with vi-mode readline (don't know about emacs-mode).

Not sure what the full extent of these problems is, but noticed a few common normal mode commands not working as expected. These include:

• A does not jump to the end of the line
• similarly, I does not jump to the beginning of the line
• t enters insert mode instead of waiting for a character and then jumping before its first occurence after the cursor. Similarly with T and F (f appears to work correctly)
• u doesn't undo the last edit
• c is a no-op instead of waiting for a movement, then changing text between cursor and movement destination

I imagine this problem is more widespread and there are other readline functionalities that don't function as expected. All of these work as expected in irb --legacy and other readline programs (e.g. bash).

Steps to reproduce

(this is all on irb-1.2.1 installed from GitHub)

To reproduce the first issue from above, set readline to vi-mode, e.g. by modifying ~/.inputrc:

set editing-mode vi

Start irb, then enter the following sequence of keystrokes:

123<escape>BA

This results in the buffer containing the following (^ indicates cursor position):

A123
 ^

in normal mode, whereas irb --legacy (or another readline program like bash) would lead to

123
   ^

in insert mode.

Start by reproducing the vi-mode cases in irb-1.2.1 with set editing-mode vi in ~/.inputrc, then compare the same keystrokes in irb --legacy or bash. Trace the readline-compatible vi-mode entry points responsible for A, I, t/T/F, u, and c; done means these commands behave as described in the issue without regressing insert mode.