[Question] How to add file to PBXNativeTarget

I'm trying to add a file (GoogleServices-Info.plist) to my main project folder, but can't figure out what function to use. I've tried every one, and the best I can do is get it into my Plugins folder. Anyone know?

I thought these might work, but they didn't:
```javascript
project.addToPbxGroupType(file, targetKey, 'PBXNativeTarget');
project.addToPbxFileReferenceSection(file);

// this one gives an error; sources is undefined
project.addToPbxCopyfilesBuildPhase(file);
```

首先检查项目中用于 PBX groups、file references 和 copy-files build phases 的 API，然后使用 GoogleServices-Info.plist 和一个 PBXNativeTarget 重现报告的行为。当正确的 target 和项目文件夹包含该文件且不再出现报告的错误，并有一个专门的测试或记录在案的用法对此进行演示时，该 issue 即完成。

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