[Fix-11583][UI] Fix the API usage of gantt graph

[lxorc]

Purpose of the pull request

Fixes #11583, the backend passed wrong data that cannot be parsed by the frontend.

(The import items were changed because of the spotless check)

Verify this pull request

This change added tests and can be verified as follows: Manually verified the change by testing locally.

[lxorc]

Please review the backend @SbloodyS

[lxorc]

@caishunfeng Please review the backend

[caishunfeng]

LGTM

[codecov-commenter]

Codecov Report

Merging #13778 (dfb5836) into dev (69e7449) will decrease coverage by 0.05%.
The diff coverage is 0.00%.

❗ Current head dfb5836 differs from pull request most recent head ab8a8a0. Consider uploading reports for the commit ab8a8a0 to get more accurate results

@@             Coverage Diff              @@
##                dev   #13778      +/-   ##
============================================
- Coverage     39.02%   38.97%   -0.05%     
+ Complexity     4450     4442       -8     
============================================
  Files          1133     1133              
  Lines         42353    42353              
  Branches       4789     4793       +4     
============================================
- Hits          16528    16507      -21     
- Misses        23999    24021      +22     
+ Partials       1826     1825       -1     

Impacted Files	Coverage Δ
...r/api/service/impl/ProcessInstanceServiceImpl.java	59.92% <0.00%> (ø)

... and 6 files with indirect coverage changes

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[sonarqubecloud]

SonarCloud Quality Gate failed.   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
16 Code Smells

12.1% Coverage
10.9% Duplication