Fix: use window ref instead of app ref to get bounds on macos

[cnwangjie]

This PR fixes the problem mentioned in the issue #210.

The problem is AXUIElementCopyAttributeValue with kAXPositionAttribute should pass a window reference in most cases.

I modified it to try to get either the focused window or the main window to ensure compatibility with multi-window scenarios without modifying the API.

Following is the test code:

package main

import (
	"fmt"

	"github.com/go-vgo/robotgo"
)

func main() {
	pid := 35866

	x, y, w, h := robotgo.GetBounds(pid)
	fmt.Printf("Window bounds: x=%d, y=%d, width=%d, height=%d\n", x, y, w, h)
}

    

Before this PR, its output was like

Window bounds: x=1933312, y=1932168, width=19, height=-1177118969

After fix

Window bounds: x=980, y=58, width=1024, height=604

[CLAassistant]

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