kern/54422: right-hand modifiers don't work for text console magic key sequences

[jdbaker%consolidated.net@localhost]

>Number:         54422
>Category:       kern
>Synopsis:       right-hand modifiers don't work for text console magic key sequences
>Confidential:   no
>Severity:       non-critical
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          change-request
>Submitter-Id:   net
>Arrival-Date:   Mon Jul 29 20:35:00 +0000 2019
>Originator:     John D. Baker
>Release:        NetBSD/i386-1.4 through 8.99.51
>Organization:
>Environment:
NetBSD skuld.technoskunk.fur 8.1_STABLE NetBSD 8.1_STABLE (SKULD) #317: Thu Jul 18 19:29:17 CDT 2019  sysop%yggdrasil.technoskunk.fur@localhost:/r0/build/netbsd-8/obj/amd64/sys/arch/amd64/compile/SKULD amd64

>Description:
This has vexed me for some time, but I just now felt compelled to
mention it.

On i386/amd64 or other ports that use a similar keyboard with wscons,
at a text console various magic key sequences only use the left-hand
modifier keys (Shift, Ctrl, Alt) while their right-hand equivalents
produce only strange character sequences.

To wit:

RShift+PgUp produces "<esc>[5~" instead of scrolling the screen back.
RShift+PgDn produces "<esc>[6~" instead of scrolling the screen forward.

Given the proximity of the PgUp/PgDn keys to the right-hand Shift key,
on the extended AT keyboard layout, it would be nice to be able to
scroll a text terminal up and down with only one hand.

Any Ctrl+Alt+Fn combination that uses the right-hand copy of either of
the modifier keys produces

 <esc>[11~
 <esc>[12~
 <esc>[13~
 <esc>[14~
 <esc>[15~

instead of switching to the desired virtual terminal or back to Xorg.
(Meanwhile Xorg allows any combination of Ctrl+Alt+Fn to switch to
any of the text screens.)

The same also may be true of "Ctrl+Alt+ESC" to enter DDB, but I'm not
in a position to test that while opening this PR.

Last I checked, FreeBSD and OpenBSD support using either left or
right-hand modifier keys on their virtual terminals.  As does
penguin-OS.
>How-To-Repeat:
See above.
>Fix: