[Bug]: StrUtf8Coder in Python can't deserialize what's encoded with Java StringUtf8Coder

### What happened?

I tried to use Python StrUtf8Coder to deserialize an string encoded with Java StringUtf8Coder but couldn't work. This is because beam is using different ways of implementation in Java and Python.

In Java, bytes length is encoded into the output bytes: https://github.com/apache/beam/blob/master/sdks/java/core/src/main/java/org/apache/beam/sdk/coders/StringUtf8Coder.java#L50 while in Python encoding is simply calling value.encode('utf-8'): https://github.com/apache/beam/blob/master/sdks/python/apache_beam/coders/coders.py#L426-L439

### Issue Priority

Priority: 3 (minor)

### Issue Components

- [X] Component: Python SDK
- [X] Component: Java SDK
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