Remove old versions of string_decoder

[amgleitman]

Please select one of the following

• I am removing an existing difference between facebook/react-native and microsoft/react-native-macos 👍
• I am cherry-picking a change from Facebook's react-native into microsoft/react-native-macos 👍
• I am making a fix / change for the macOS implementation of react-native
• I am making a change required for Microsoft usage of react-native

Summary

We're still holding on to an old version of string_decoder in some places. We get rid of them by doing the following:

• For the one in bots/, we have this dependency because of firebase, and even the latest version of firebase depends on the old string_decoder, so the solution here is to resolve readable-stream (the module that actually pulls in string_decoder) to at least 4.0.0 (similar to what we had to do in Resolve readable-stream to 4.0.0 #1252).
• For the one in ReactCommon/hermes/inspector/tools/msggen/, we just need to upgrade webpack to the latest version and we're all set.

[amgleitman]

/azp run

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Azure Pipelines successfully started running 3 pipeline(s).

[amgleitman]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 3 pipeline(s).