Rename some variables to avoid possible confusion between Result and AppResponse.

[chickenlj]

What is the purpose of the change

Rename some variables to avoid possible confusion between Result and AppResponse.

Brief changelog

XXXXX

Verifying this change

XXXXX

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[codecov-io]

Codecov Report

Merging #3889 into 3.x-dev will increase coverage by 0.09%.
The diff coverage is 58.82%.

@@              Coverage Diff              @@
##             3.x-dev    #3889      +/-   ##
=============================================
+ Coverage      63.62%   63.71%   +0.09%     
  Complexity        71       71              
=============================================
  Files            706      706              
  Lines          31072    31072              
  Branches        5029     5029              
=============================================
+ Hits           19769    19797      +28     
+ Misses          9023     8998      -25     
+ Partials        2280     2277       -3

Impacted Files	Coverage Δ	Complexity Δ
...ava/org/apache/dubbo/rpc/filter/TimeoutFilter.java	66.66% <ø> (ø)	0 <0> (ø)	⬇️
...bo/rpc/cluster/support/FailsafeClusterInvoker.java	100% <ø> (ø)	0 <0> (ø)	⬇️
...org/apache/dubbo/rpc/filter/ActiveLimitFilter.java	95.45% <ø> (ø)	0 <0> (ø)	⬇️
...rg/apache/dubbo/rpc/filter/ExecuteLimitFilter.java	76.19% <ø> (ø)	0 <0> (ø)	⬇️
...apache/dubbo/rpc/filter/ConsumerContextFilter.java	100% <100%> (ø)	0 <0> (ø)	⬇️
...ava/org/apache/dubbo/rpc/filter/ContextFilter.java	91.17% <100%> (ø)	0 <0> (ø)	⬇️
...main/java/org/apache/dubbo/rpc/AsyncRpcResult.java	56.16% <33.33%> (ø)	0 <0> (ø)	⬇️
...org/apache/dubbo/rpc/filter/GenericImplFilter.java	56.38% <62.5%> (ø)	0 <0> (ø)	⬇️
.../org/apache/dubbo/rpc/filter/CompatibleFilter.java	60% <66.66%> (ø)	0 <0> (ø)	⬇️
...a/org/apache/dubbo/rpc/filter/ExceptionFilter.java	60.52% <66.66%> (ø)	0 <0> (ø)	⬇️
... and 10 more

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[carryxyh]

LGTM.
It seems to be clear that the Result of the call back is actually an appresponse.

If it is not for compatibility reasons, I agree to remove the Result interface of the appResponse.