RFR: 8243208: Clean up JVMFlag implementation [v3]

[Ioi Lam]

On Wed, 9 Sep 2020 14:09:23 GMT, Coleen Phillimore <coleenp at openjdk.org> wrote:

>> Ioi Lam has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Fixed JVMFlag::is_writeable()
>
> src/hotspot/share/runtime/flags/jvmFlag.hpp line 36:
> 
>> 34: typedef const char* (*RangeStrFunc)(void);
>> 35:
>> 36: struct JVMFlag {
> 
> I'm still getting used to git diffs, but can you change this from struct to class?  Because it looks like it does have
> private and public sections.

I want to limit the changes in this PR, so I plan to do this in a future RFE, probably
[JDK-8081833](https://bugs.openjdk.java.net/browse/JDK-8081833). I'll also change all the fields to private, and add
accessor methods to them. And also add proper iterators for the flags (instead of walking JVMFlag::flags[] directly).

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PR: https://git.openjdk.java.net/jdk/pull/82