Add key combinations for ctrl-delete and shift-delete (#3284)

Currently there is not option to bind ctrl-delete and shift-delete. As
suggested by issue #3240, shift-delete could be used to bind "delete
entry from history" as it is a common way to do so in other
applications, e.g. browsers.

This, however, does only implement to use the key combination itself and
does not assign a default action to any of them. This does enable to
call one's all predefined actions. With the exec action this can
expanded like the issue #3240 suggested.
If desirable, the key combinations could later get a default behavior.

Co-authored-by: Junegunn Choi <junegunn.c@gmail.com>

test/test_go.rb

@@ -2922,6 +2922,15 @@ class TestGoFZF < TestBase
     tmux.until { assert_block(expected, _1) }
   end
 
+  def test_delete_with_modifiers
+    tmux.send_keys "seq 100 | #{FZF} --bind 'ctrl-delete:up+up,shift-delete:down,focus:transform-prompt:echo [{}]'", :Enter
+    tmux.until { |lines| assert_equal 100, lines.item_count }
+    tmux.send_keys 'C-Delete'
+    tmux.until { |lines| assert_equal '[3]', lines[-1] }
+    tmux.send_keys 'S-Delete'
+    tmux.until { |lines| assert_equal '[2]', lines[-1] }
+  end
+
   def test_become_tty
     tmux.send_keys "sleep 0.5 | #{FZF} --bind 'start:reload:ls' --bind 'load:become:tty'", :Enter
     tmux.until { |lines| assert_includes lines, '/dev/tty' }