Restructure core:terminal for better Windows support

core/terminal/terminal_windows.odin

@@ -1,3 +1,4 @@
+#+private
 package terminal
 
 import "core:os"
@@ -7,3 +8,53 @@ _is_terminal :: proc(handle: os.Handle) -> bool {
 	is_tty := windows.GetFileType(windows.HANDLE(handle)) == windows.FILE_TYPE_CHAR
 	return is_tty
 }
+
+old_modes: [2]struct{
+	handle: windows.DWORD,
+	mode: windows.DWORD,
+} = {
+	{windows.STD_OUTPUT_HANDLE, 0},
+	{windows.STD_ERROR_HANDLE, 0},
+}
+
+@(init)
+_init_terminal :: proc() {
+	vtp_enabled: bool
+
+	for &v in old_modes {
+		handle := windows.GetStdHandle(v.handle)
+		if handle == windows.INVALID_HANDLE || handle == nil {
+			return
+		}
+		if windows.GetConsoleMode(handle, &v.mode) {
+			windows.SetConsoleMode(handle, v.mode | windows.ENABLE_VIRTUAL_TERMINAL_PROCESSING)
+
+			new_mode: windows.DWORD
+			windows.GetConsoleMode(handle, &new_mode)
+
+			if new_mode & windows.ENABLE_VIRTUAL_TERMINAL_PROCESSING != 0 {
+				vtp_enabled = true
+			}
+		}
+	}
+
+	if vtp_enabled {
+		// This color depth is available on Windows 10 since build 10586.
+		color_depth = .Four_Bit
+	} else {
+		// The user may be on a non-default terminal emulator.
+		color_depth = get_environment_color()
+	}
+}
+
+@(fini)
+_fini_terminal :: proc() {
+	for v in old_modes {
+		handle := windows.GetStdHandle(v.handle)
+		if handle == windows.INVALID_HANDLE || handle == nil {
+			return
+		}
+		
+		windows.SetConsoleMode(handle, v.mode)
+	}
+}