Add Windows support to g_get_os_info()

Most of the info returned is static, the only thing that changes
is the OS version.

This code relies on g_win32_check_windows_version() providing
accurate information (hopefully, MS won't nix RtlGetVersion() on
which we use for that) and supplements it with information from the
registry for Windows >= 8.1.
11 jobs for osinfo in 51 minutes and 50 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Build
passed #461398
cross-android_api21_arm64

00:01:38

passed #461399
cross-android_api28_arm64

00:02:10

passed #461400
cross-mingw64

00:02:11

passed #461396
debian-stable-x86_64

00:02:20

passed #461395
fedora-x86_64

00:04:18

passed #461397
G_DISABLE_ASSERT

00:03:57

passed #461401
win32
msys2-mingw32

00:12:34

passed #461402
win32
vs2017-x64

00:09:33

 
  Coverage
passed #461403
coverage

00:01:12

77.9%
 
  Analysis
passed #461405
scan-build

00:38:02

failed #461404
allowed to fail
valgrind

00:35:19

 
Name Stage Failure
failed
valgrind Analysis
Uploading artifacts...
_build/config.h: found 1 matching files
_build/glib/glibconfig.h: found 1 matching files

_build/meson-logs: found 7 matching files

Uploading artifacts to coordinator... ok
id=461404 responseStatus=201 Created token=X2CGzJxg
Uploading artifacts...
_build/valgrind-report.xml: found 1 matching files

Uploading artifacts to coordinator... ok
id=461404 responseStatus=201 Created token=X2CGzJxg
ERROR: Job failed: exit code 1