improve error message in NativeModuleRegistryBuilder.java

[vonovak]

Motivation

I have seen a spike in users reporting this error. Unfortunately I did not receive any repros that would confirm this, but my hypothesis is that they ran into situation when new XYZPackage() was present in getPackages() method and then the CLI kicked in with autolinking and they were left with this incomplete error.

someone more knowledgeable of autolinking should review this.

[pull-bot]

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Generated by 🚫 dangerJS against 48d4d2f

[cpojer]

Thanks for updating the error message!

[facebook-github-bot]

@cpojer is landing this pull request. If you are a Facebook employee, you can view this diff on Phabricator.

[react-native-bot]

This pull request was successfully merged by @vonovak in 113c4e2.

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