Add ctrl-alt-h compatibility binding

Historically, ctrl-i sends the same code as tab, ctrl-h sends backspace and
ctrl-j and ctrl-m behave like enter.

Even for terminals that send unambiguous encodings (via the kitty keyboard
protocol), we have kept bindings like ctrl-h, to support existing habits.

We forgot that pressing alt-ctrl-h would behave like alt-backspace (and can
be easier to reach) so maybe we should add that as well.

Don't add ctrl-shift-i because at least on Linux, that's usually intercepted
by the terminal emulator.

Technically there are some more such as "ctrl-2" (which used to do the same as
"ctrl-space") but I don't think anyone uses that over "ctrl-space".

Closes #https://github.com/fish-shell/fish-shell/discussions/11548

(cherry picked from commit 4d67ca7c58)

share/functions/fish_default_key_bindings.fish

@@ -58,6 +58,7 @@ function fish_default_key_bindings -d "emacs-like key binds"
 
     bind --preset $argv alt-c capitalize-word
     bind --preset $argv alt-backspace backward-kill-word
+    bind --preset $argv ctrl-alt-h backward-kill-word
     bind --preset $argv ctrl-backspace backward-kill-word
     bind --preset $argv ctrl-delete kill-word