windows: add window handle related system calls

https://docs.microsoft.com/en-us/windows/win32/api/winuser/nf-winuser-enumwindows
https://docs.microsoft.com/en-us/windows/win32/api/winuser/nf-winuser-enumchildwindows
https://docs.microsoft.com/en-us/windows/win32/api/winuser/nf-winuser-getclassnamew
https://docs.microsoft.com/en-us/windows/win32/api/winuser/nf-winuser-getdesktopwindow
https://docs.microsoft.com/en-us/windows/win32/api/winuser/nf-winuser-getforegroundwindow
https://docs.microsoft.com/en-us/windows/win32/api/winuser/nf-winuser-iswindow
https://docs.microsoft.com/en-us/windows/win32/api/winuser/nf-winuser-iswindowunicode
https://docs.microsoft.com/en-us/windows/win32/api/winuser/nf-winuser-iswindowvisible
https://docs.microsoft.com/en-us/windows/win32/api/winuser/nf-winuser-getguithreadinfo

Change-Id: I21fbf47e1f459e86503e0e876b44cf47c98b2aa0
GitHub-Last-Rev: 242b79f
GitHub-Pull-Request: #122
Reviewed-on: https://go-review.googlesource.com/c/sys/+/399134
Auto-Submit: Alex Brainman <alex.brainman@gmail.com>
Reviewed-by: Benny Siegert <bsiegert@gmail.com>
Reviewed-by: Than McIntosh <thanm@google.com>
Reviewed-by: Alex Brainman <alex.brainman@gmail.com>
Run-TryBot: Alex Brainman <alex.brainman@gmail.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

Author: ToadKing

windows/syscall_windows.go

@@ -364,6 +364,15 @@ func NewCallbackCDecl(fn interface{}) uintptr {
 //sys	SetCommTimeouts(handle Handle, timeouts *CommTimeouts) (err error)
 //sys	GetActiveProcessorCount(groupNumber uint16) (ret uint32)
 //sys	GetMaximumProcessorCount(groupNumber uint16) (ret uint32)
+//sys	EnumWindows(enumFunc uintptr, param unsafe.Pointer) (err error) = user32.EnumWindows
+//sys	EnumChildWindows(hwnd HWND, enumFunc uintptr, param unsafe.Pointer) = user32.EnumChildWindows
+//sys	GetClassName(hwnd HWND, className *uint16, maxCount int32) (copied int32, err error) = user32.GetClassNameW
+//sys	GetDesktopWindow() (hwnd HWND) = user32.GetDesktopWindow
+//sys	GetForegroundWindow() (hwnd HWND) = user32.GetForegroundWindow
+//sys	IsWindow(hwnd HWND) (isWindow bool) = user32.IsWindow
+//sys	IsWindowUnicode(hwnd HWND) (isUnicode bool) = user32.IsWindowUnicode
+//sys	IsWindowVisible(hwnd HWND) (isVisible bool) = user32.IsWindowVisible
+//sys	GetGUIThreadInfo(thread uint32, info *GUIThreadInfo) (err error) = user32.GetGUIThreadInfo
 
 // Volume Management Functions
 //sys	DefineDosDevice(flags uint32, deviceName *uint16, targetPath *uint16) (err error) = DefineDosDeviceW

windows/types_windows.go

@@ -3213,3 +3213,22 @@ type ModuleInfo struct {
 }
 
 const ALL_PROCESSOR_GROUPS = 0xFFFF
+
+type Rect struct {
+	Left   int32
+	Top    int32
+	Right  int32
+	Bottom int32
+}
+
+type GUIThreadInfo struct {
+	Size        uint32
+	Flags       uint32
+	Active      HWND
+	Focus       HWND
+	Capture     HWND
+	MenuOwner   HWND
+	MoveSize    HWND
+	CaretHandle HWND
+	CaretRect   Rect
+}