Optimize the logic of obtaining the mock parameter value in the MockInvoker#invoke method

[BurningCN]

The logic of the original code can be replaced with the getMethodParameter method. The logic of the getMethodParameter method is as follows:
For example, URL url = "test://1.1.1.1/path?test.mock=xx&mock=yy", url.getMethodParameter("test","mock") will first get the parameter value of test.mock,if it does not exist,, then Get the mock parameter value directly

[codecov-commenter]

Codecov Report

Merging #7840 (81211aa) into master (e845e16) will increase coverage by 0.14%.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##             master    #7840      +/-   ##
============================================
+ Coverage     59.28%   59.42%   +0.14%     
- Complexity      529      557      +28     
============================================
  Files          1077     1086       +9     
  Lines         43565    43844     +279     
  Branches       6368     6381      +13     
============================================
+ Hits          25826    26055     +229     
- Misses        14879    14907      +28     
- Partials       2860     2882      +22     

Impacted Files	Coverage Δ	Complexity Δ
...java/org/apache/dubbo/rpc/support/MockInvoker.java	84.61% <100.00%> (-0.51%)	0.00 <0.00> (ø)
...ntext/event/AwaitingNonWebApplicationListener.java	48.48% <0.00%> (-24.25%)	0.00% <0.00%> (ø%)
.../dubbo/remoting/transport/MultiMessageHandler.java	80.00% <0.00%> (-20.00%)	0.00% <0.00%> (ø%)
...bo/rpc/cluster/support/FailbackClusterInvoker.java	52.45% <0.00%> (-18.04%)	0.00% <0.00%> (ø%)
...va/org/apache/dubbo/rpc/support/ProtocolUtils.java	61.53% <0.00%> (-8.03%)	0.00% <0.00%> (ø%)
...ng/transport/dispatcher/all/AllChannelHandler.java	82.75% <0.00%> (-6.90%)	0.00% <0.00%> (ø%)
...dubbo/remoting/exchange/support/DefaultFuture.java	80.34% <0.00%> (-6.84%)	0.00% <0.00%> (ø%)
.../threadpool/manager/DefaultExecutorRepository.java	80.95% <0.00%> (-4.54%)	0.00% <0.00%> (ø%)
.../rpc/protocol/dubbo/LazyConnectExchangeClient.java	49.45% <0.00%> (-4.40%)	0.00% <0.00%> (ø%)
.../apache/dubbo/remoting/transport/AbstractPeer.java	58.69% <0.00%> (-4.35%)	0.00% <0.00%> (ø%)
... and 88 more

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