test: add unit test for common module

[liuqiufeng]

• I have registered the PR changes.

Ⅰ. Describe what this PR did

add unit test for
EnhancedServiceLoader,ExtensionDefinition,SizeUtilTest,ReflectionUtil,LowerCaseLinkHashMap,FileLoader,ObjectHolder

io.seata.common.loader.EnhancedServiceLoaderTest#testUnloadByClassAndActivateName需要等EnhancedServiceLoader改造后才能启用

Ⅱ. Does this pull request fix one issue?

fixes #5305

Ⅲ. Why don't you add test cases (unit test/integration test)?

Ⅳ. Describe how to verify it

Ⅴ. Special notes for reviews

[codecov-commenter]

Codecov Report

Merging #5335 (5fa66b2) into 2.x (51f6a09) will increase coverage by 0.32%.
The diff coverage is n/a.

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@@             Coverage Diff              @@
##                2.x    #5335      +/-   ##
============================================
+ Coverage     48.67%   49.00%   +0.32%     
- Complexity     4259     4307      +48     
============================================
  Files           769      769              
  Lines         27183    27183              
  Branches       3379     3379              
============================================
+ Hits          13232    13320      +88     
+ Misses        12562    12467      -95     
- Partials       1389     1396       +7     

Impacted Files	Coverage Δ
...er/src/main/java/io/seata/server/ServerRunner.java	50.00% <0.00%> (-15.39%)	⬇️
.../java/io/seata/server/coordinator/DefaultCore.java	47.30% <0.00%> (-3.60%)	⬇️
...o/seata/server/session/AbstractSessionManager.java	62.31% <0.00%> (-2.90%)	⬇️
...rage/redis/store/RedisTransactionStoreManager.java	76.34% <0.00%> (-0.78%)	⬇️
...in/java/io/seata/server/session/BranchSession.java	78.57% <0.00%> (-0.72%)	⬇️
...in/java/io/seata/server/session/GlobalSession.java	69.92% <0.00%> (-0.38%)	⬇️
...erver/storage/file/session/FileSessionManager.java	49.68% <0.00%> (+0.63%)	⬆️
...va/io/seata/common/loader/ExtensionDefinition.java	45.16% <0.00%> (+6.45%)	⬆️
.../io/seata/common/loader/EnhancedServiceLoader.java	65.08% <0.00%> (+7.75%)	⬆️
...n/src/main/java/io/seata/common/io/FileLoader.java	68.42% <0.00%> (+10.52%)	⬆️
... and 3 more

[slievrly]

LGTM, Pls add change.

[liuqiufeng]

LGTM, Pls add change.

done.

[funky-eyes]

LGTM