Share alt-{b,f} with Vi mode, to work around Terminal.app/Ghostty more

Commit f4503af037 (Make alt-{b,f} move in directory history if commandline is
empty, 2025-01-06) had the intentional side effect of making alt-{left,right}
(move in directory history) work in Terminal.app and Ghostty without other,
less reliable workarounds.
That commit says "that [workaround] alone should not be the reason for
this change."; maybe this was wrong.

Extend the workaround to Vi mode.  The intention here is to provide
alt-{left,right} in Vi mode.  This also adds alt-{b,f} which is odd but
mostly harmless (?) because those don't do anything else in Vi mode.
It might be confusing when studying "bind" output but that one already has
almost 400 lines for Vi mode.

Closes #11479

(cherry picked from commit 3081d0157b)

share/functions/__fish_shared_key_bindings.fish

@@ -59,6 +59,9 @@ function __fish_shared_key_bindings -d "Bindings shared between emacs and vi mod
     $legacy_bind --preset $argv \e\[1\;9C nextd-or-forward-word # iTerm2 < 3.5.12
     $legacy_bind --preset $argv \e\[1\;9D prevd-or-backward-word # iTerm2 < 3.5.12
 
+    bind --preset $argv alt-b prevd-or-backward-word
+    bind --preset $argv alt-f nextd-or-forward-word
+
     bind --preset $argv alt-up history-token-search-backward
     bind --preset $argv alt-down history-token-search-forward
     $legacy_bind --preset $argv \e\[1\;9A history-token-search-backward # iTerm2 < 3.5.12

share/functions/fish_default_key_bindings.fish

@@ -60,8 +60,6 @@ function fish_default_key_bindings -d "emacs-like key binds"
     bind --preset $argv alt-backspace backward-kill-word
     bind --preset $argv ctrl-backspace backward-kill-word
     bind --preset $argv ctrl-delete kill-word
-    bind --preset $argv alt-b prevd-or-backward-word
-    bind --preset $argv alt-f nextd-or-forward-word
 
     bind --preset $argv alt-\< beginning-of-buffer
     bind --preset $argv alt-\> end-of-buffer