RFR: 8258961: move some fields of SafePointNode from public to protected

[Xin Liu]

On Wed, 6 Jan 2021 09:15:24 GMT, Tobias Hartmann <thartmann at openjdk.org> wrote:

>> Declare VMStructs is a friend of SafePointNode so we can move some fields from public zone to protected zone. 
>> Clean up the forward declaration section in callnode.hpp. Lock/Unlock Nodes are subclasses of AbstractLockNode.
>
> @navyxliu There is a title mismatch between the PR and the JBS issue that you need to fix before integration.

hello, @TobiHartmann , 
Could you take a look at this PR again?  I've corrected title and description to reflect what this patch does.

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PR: https://git.openjdk.java.net/jdk/pull/1899