Currently, Unsafe.makePrivateBuffer returns an inline type. As a result, C2 attempts scalarization which leads to incorrect results.

We would need to:
- Make sure private buffers are never scalarized (also not in safepoints)
- Be careful when removing redundant allocations to not replace larval buffer allocations by "normal" buffer allocations
- Make sure the Unsafe.get*/put* operations have an effect
- Scalarize only after finishPrivateBuffer

This manifests, for example, with TestIntrinsics when being executed with -XX:DisableIntrinsic=_putInt because the call to Unsafe.putInt has no effect on the scalarized inline type.

Also, code like this currently crashes C2's typesystem:
    MyValue incrementAndCheckUnsafe() {
        MyValue vt = U.makePrivateBuffer(this);
        U.putInt(vt, X_OFFSET, x + 1);
        U.putInt(vt, Y_OFFSET, y + 1);
        return vt;
    }

This also manifests with tests being executed with -XX:+DeoptimizeALot.