Move supported operating system check out of SystemInfo constructor (#1680)
Move supported operating system check out of SystemInfo constructor (#1680)

* Initialization timing issue for static variable

currentPlatform variable initialized in static block of this class.
But it's also accessed via constructor for validate unsupported environment.
This variable possible not initialized yet when access make a instance use constructor.
I'm already met this kind of issue when I run unit test use this library.
I think one more variable init checking required, at least If constructor want to check unsupported or not.

* Initialize static variable from static method instead of static block

* Initialize static variable from static method instead of static block

#1671 not worked for me.
Run CI with snapshot version but I saw same error message below.
```
[ERROR] display as string  Time elapsed: 0.016 s  <<< ERROR!
java.lang.UnsupportedOperationException: Operating system not supported: JNA Platform type 2
Caused by: java.lang.UnsupportedOperationException: Operating system not supported: JNA Platform type 2
```
JNA could recognize current os in static block when failed on a constructor of SystemInfo class.
So I tried check unknown environment by JNA method instead of OSHI. At the result my CI passed successfully.
I'm not sure what is exact reason. But I just think that JNA and OSHI depends on many static initialization and it's make not easy to assume proper working.

In my opinion, static blocks and variables should be minimized.
But if OSHI have important reason to check unsupported environment in constructor this MR need to approved.

There is remained riddle why OSHI's static variable and JNA static method result don't have consistency.
Anyway, This change working for me.
Please consider enough.

* Update SystemInfo.java

* Add comment to explain why constructor is empty

Co-authored-by: sam <f16bed56189e249fe4ca8ed10a1ecae60e8ceac0@jennifersoft.com>
Co-authored-by: Daniel Widdis <ed65046fad445dfc08f8520992732af46ed3ee7e@gmail.com>
dbwiddis/oshi,hazendaz/oshi