8353729: Add unsynchronized variant of ByteArrayOutputStream

[jengebr]

Adds the method ByteArrayOutputStream.unsynchronized, which predictably returns an unsynchronized variant of same. Benchmark (included) shows up to 4x improvement when making many small writes, such as via write(int) or repeated small buffers. No other impacts observed.

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Progress

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Issue

• JDK-8353729: Add unsynchronized variant of ByteArrayOutputStream (Enhancement - P4)

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