fix: use package.json as sole indicator of project existence

[luo2430]

fix an issue

PS C:\Users\24306\cocos-project> cocos create --project .

Creating project...
Path: C:\Users\24306\cocos-project
Type: 3d
Warning: target path already exists, will try to create inside it.
Error: Failed to create project, project exist
    at Project.create (C:\Users\24306\git_learning\cocos-cli\dist\core\project\script\index.js:60:23)
    at ProjectManager.create (C:\Users\24306\git_learning\cocos-cli\dist\core\project-manager.js:58:30)
    at process.processTicksAndRejections (node:internal/process/task_queues:103:5)
    at async CocosAPI.createProject (C:\Users\24306\git_learning\cocos-cli\dist\api\index.js:110:16)
    at async Command.<anonymous> (C:\Users\24306\git_learning\cocos-cli\dist\commands\create.js:66:28)
✗ Failed to create project.