Copy stable/9 to releng/9.3 as part of the 9.3-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

MFC 219886, 226100, 226111, 226341, 242529, 259015, 259016, 259019, 259049,
259071, 259102, 259110, 259129, 259130, 259178, 259179, 259203, 259221,
259261, 259532, 259615, 259650, 259651, 259667, 259680, 259727, 259761,
259772, 259776, 259777, 259830, 259882, 259915, 260160, 260449, 260450,
260688, 260888, 260953, 261269, 261547, 261551, 261552, 261553, 261585
o Merge vt(4) virtual terminal (a.k.a. newcons) to stable/9.
o Merge teken updates.
o Add few more tty methods required by vt(4).
o Update syscons(4) to work with fresh teken.

Sponsored by: The FreeBSD Foundation

Merge VT(9) project (a.k.a. newcons).

Reviewed by: nwhitehorn
MFC_to_10_after: re approval

Sponsored by: The FreeBSD Foundation

Notify terminal about process on current terminal start to use mouse on a
different "mouse level".

Sponsored by: The FreeBSD Foundation

Move vt_mouse_event out of sysmouse lock.

Sponsored by: The FreeBSD Foundation

o Remove include of sys/mouse.h, it is included from vt.h now.
o Call vt_mouse_event method, to notify VT(9) about mouse events.
o Add empty MOUSE_MOUSECHAR ioctl handler.
o Remove trailing whitespace.

Sponsored by: The FreeBSD Foundation

MFC @r256953

Readd the vt(4) driver and corresponding tools.