[ISSUE #4621] Implement TransformerEngine for EventMesh Transformer

[xwm1992]

Fixes #4621 .

Motivation

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Modifications

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Documentation

• Does this pull request introduce a new feature? (yes / no)
• If yes, how is the feature documented? (not applicable / docs / JavaDocs / not documented)
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[codecov]

Codecov Report

Attention: 95 lines in your changes are missing coverage. Please review.

Comparison is base (6508df8) 16.80% compared to head (40f1098) 16.90%.
Report is 6 commits behind head on master.

Files	Patch %	Lines
...ache/eventmesh/runtime/boot/TransformerEngine.java	0.00%	56 Missing ⚠️
.../core/protocol/http/push/AsyncHTTPPushRequest.java	0.00%	12 Missing ⚠️
.../apache/eventmesh/transformer/TransformerType.java	41.17%	10 Missing ⚠️
...otocol/http/processor/SendAsyncEventProcessor.java	0.00%	6 Missing ⚠️
...apache/eventmesh/transformer/TransformerParam.java	77.77%	4 Missing ⚠️
...he/eventmesh/runtime/boot/EventMeshHTTPServer.java	0.00%	3 Missing ⚠️
...ache/eventmesh/transformer/TransformerBuilder.java	60.00%	1 Missing and 1 partial ⚠️
...ava/org/apache/eventmesh/transformer/Template.java	50.00%	0 Missing and 1 partial ⚠️
...ava/org/apache/eventmesh/transformer/Variable.java	75.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #4622      +/-   ##
============================================
+ Coverage     16.80%   16.90%   +0.10%     
- Complexity     1678     1703      +25     
============================================
  Files           782      790       +8     
  Lines         29317    29522     +205     
  Branches       2532     2550      +18     
============================================
+ Hits           4926     4991      +65     
- Misses        23932    24065     +133     
- Partials        459      466       +7     

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[pandaapo]

Should this step be placed before for( ), otherwise, is it possible for metaServiceListener to be null when addTransformerListener() in updateTransformerMap()?

这一步是不是应该放到for( )前面，否则的话，updateTransformerMap()中addTransformerListener()时，metaServiceListener是不是为null？