improve isWindows method in HashedWheelTimer

[zx844174097]

Memory usage is too high。frequently GC

发现所有分支皆有此问题，则提交到主分支

#6820
#6808

bug 所在文件 https://github.com/apache/dubbo/blob/master/dubbo-common/src/main/java/org/apache/dubbo/common/timer/HashedWheelTimer.java

出现问题的方法:
private boolean isWindows() { return System.getProperty("os.name", "").toLowerCase(Locale.US).contains("win"); }
问题产生原因：
1.waitForNextTick() 中无限调用 isWindows();

2.toLowerCase(Locale.US) 将急速产生 char[] 对象。导致内存占用过高。

解决方案：
` private static boolean isWindows = System.getProperty("os.name", "").toLowerCase(Locale.US).contains("win");

private boolean isWindows() {
return isWindows;
}`

close #6820

[htynkn]

this change makes sense to me and will merge soon when CI pass.

Another thing is current way to check OS maybe not good enough. there are many utils can do similar work:

• https://github.com/apache/commons-lang/blob/master/src/main/java/org/apache/commons/lang3/SystemUtils.java

Maybe this is something we can improve in the future

[codecov-io]

Codecov Report

Merging #6845 into master will decrease coverage by 0.14%.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##             master    #6845      +/-   ##
============================================
- Coverage     59.15%   59.00%   -0.15%     
+ Complexity      510      506       -4     
============================================
  Files          1028     1028              
  Lines         41534    41535       +1     
  Branches       6041     6041              
============================================
- Hits          24570    24509      -61     
- Misses        14194    14244      +50     
- Partials       2770     2782      +12     

Impacted Files	Coverage Δ	Complexity Δ
...rg/apache/dubbo/common/timer/HashedWheelTimer.java	62.88% <100.00%> (-0.57%)	0.00 <0.00> (ø)
...rg/apache/dubbo/remoting/utils/PayloadDropper.java	15.38% <0.00%> (-30.77%)	0.00% <0.00%> (ø%)
...ng/transport/dispatcher/all/AllChannelHandler.java	62.06% <0.00%> (-13.80%)	0.00% <0.00%> (ø%)
...he/dubbo/common/threadpool/ThreadlessExecutor.java	52.17% <0.00%> (-10.87%)	0.00% <0.00%> (ø%)
.../apache/dubbo/rpc/protocol/AsyncToSyncInvoker.java	62.06% <0.00%> (-10.35%)	0.00% <0.00%> (ø%)
...e/dubbo/remoting/transport/netty/NettyChannel.java	52.27% <0.00%> (-7.96%)	19.00% <0.00%> (-2.00%)
.../registry/multicast/MulticastServiceDiscovery.java	23.07% <0.00%> (-7.70%)	0.00% <0.00%> (ø%)
.../org/apache/dubbo/remoting/ExecutionException.java	15.78% <0.00%> (-5.27%)	0.00% <0.00%> (ø%)
...mmon/threadpool/support/AbortPolicyWithReport.java	85.00% <0.00%> (-5.00%)	0.00% <0.00%> (ø%)
.../apache/dubbo/remoting/transport/AbstractPeer.java	58.69% <0.00%> (-4.35%)	0.00% <0.00%> (ø%)
... and 12 more

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[htynkn]

thanks for your contribution :)