term: don't respond with terminal colors to all OSC 11 queries

OSC11 allows to both query and set background color. The programs
that try to set the color, for example, 'fish' shell, don't expect
the terminal to answer with the current background color. This results
in 'fish' putting the response onto the command line.

So only respond if OSC11 payload is '?', otherwise simply ignore the
command.

In future this can be extended to passthrough OSC11 to the underlying
terminal to change its background color.

vxfw(List): add `Gap` between list items

feat(vxfw.list): add arrow key events

Downgrade to go 1.18

Successfully tested with

    GOTOOLCHAIN=go1.18.10 go build ./...

vxfw: add Suspend and Resume

vaxis: add CanRGB RGB color support getter

term: support OSC 10 queries

Similar to OSC 11.

See: ad972cce6e722423feddae782a799682779c7d25

vxfw(List): add mouse handling

vxfw(List): add SetPendingScroll

vxfw: fallback to focusing the root widget

feat(vxfw/list): ability to set cursor

This allows end-developers the ability to set the currently selected
list item.

vxfw(RichText): fix findContainerSize

Return when we should have been returning

vxfw: hide cursor before render

vxfw: clear window before rendering

vxfw: add Center and Button

vxfw: implement filling a surface

vxfw(Text): fix findContainerSize for soft wrapped text

Return the size in our branch

vxfw: fix where we set the focused widget

vxfw: implicitly set redraw on DebugCmd

vxfw: add debug print