Open Windows console handle to retreive dimensions

If stdout is redirected on Windows, the dimensions of the terminal
won't be correctly retreived. Open the console instead, using the
special filename CONOUT$, and ask the dimensions of this handle.
Keep a fallback to stdout if the console can't be opened.

https://learn.microsoft.com/en-us/windows/console/console-handles

Author: MisterDA

Diff for: src/alcotest/alcotest_stubs.c

@@ -35,8 +35,16 @@ CAMLprim value ocaml_alcotest_get_terminal_dimensions(value unit)
 	CAMLparam1(unit);
 	CAMLlocal2(result, pair);
 
+	HANDLE console = CreateFileW(L"CONOUT$", GENERIC_READ|GENERIC_WRITE,
+		FILE_SHARE_READ | FILE_SHARE_WRITE, NULL,
+		OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL);
+	HANDLE handle = console == INVALID_HANDLE_VALUE ?
+		GetStdHandle(STD_OUTPUT_HANDLE) : console;
 	CONSOLE_SCREEN_BUFFER_INFO csbi;
-	int success = GetConsoleScreenBufferInfo(GetStdHandle(STD_OUTPUT_HANDLE), &csbi);
+	int success = GetConsoleScreenBufferInfo(handle, &csbi);
+	if (console != INVALID_HANDLE_VALUE)
+            CloseHandle(console);
+
 	if (success)
 	{
 		pair = caml_alloc_tuple(2);