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

Add new terminal method terminal_set_winsize_blank. Same as terminal_set_winsize,
but with optional blank. That will allow us to see early messages after attach
more specific driver.

Sponsored by: The FreeBSD Foundation

o Rename methods according to "consdev style".
o Add cngrab/cnungrab methods.
o Allow later console attach with termcn_cnregister().

Sponsored by: The FreeBSD Foundation

Readd the vt(4) driver and corresponding tools.