fix: fix new File by only fileName

[LittleXianyu]

No description provided.

[LittleXianyu]

fix #2148

[ball-hayden]

Resolves #2138
Resolves #2136
Probably resolves #2095

To provide a bit more information on why this change is necessary:
https://github.com/microsoft/react-native-code-push/pull/2132/files changed the return value of FileUtils. validateFileName to also include the absolute path to the file, while previously it was a relative path.

The directory is then concatenated again to the file name when it is unzipped:

react-native-code-push/android/app/src/main/java/com/microsoft/codepush/react/FileUtils.java

Lines 158 to 159 in b9fb9fb

	String fileName = validateFileName(entry.getName(), destinationFolder);
	File file = new File(destinationFolder, fileName);

This doesn't affect JS bundles, as CodePush searches for a bundle as deep as it needs to (findJSBundleInUpdateContents).
For a diff update,

react-native-code-push/android/app/src/main/java/com/microsoft/codepush/react/CodePushUpdateManager.java

Lines 237 to 239 in b9fb9fb

	String diffManifestFilePath = CodePushUtils.appendPathComponent(unzippedFolderPath,
	CodePushConstants.DIFF_MANIFEST_FILE_NAME);
	boolean isDiffUpdate = FileUtils.fileAtPathExists(diffManifestFilePath);

incorrectly returns false as the diff manifest file is actually nested much deeper than we expected. This results in anything other than the jsbundle being "lost".

[ball-hayden]

@andreidubov (as the introducer of the bug) or @alexandergoncharov (as an approver) - please could you review this fix?
CodePush for Android really is quite broken at the moment, because of #2132.

[alexandergoncharov-zz]

@LittleXianyu Thanks for contributing!

@ball-hayden Thanks for describing this PR!

You guys are awesome :)

[evelant]

@alexandergoncharov This apparently didn't fix the issue. Still seeing it on 7.0.4. Images disappear on android after a 2nd push is applied.