feat: add getParentNode interface for folderTreeService

[mumiao]

Description

there is a easier way to get the current treeNode's parentNode?

Fixes #723

Changes

Please describe the changes, help the reviewer to read your code.

• add getParentNode interface for folderTreeService
• add Unit test for folderTreeService.getParentNode

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• Any dependent changes have been merged and published in downstream modules

[codecov]

Codecov Report

Merging #752 (f5052ee) into main (52d79b0) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #752      +/-   ##
==========================================
+ Coverage   91.38%   91.39%   +0.01%     
==========================================
  Files         189      189              
  Lines        5952     5959       +7     
  Branches     1428     1431       +3     
==========================================
+ Hits         5439     5446       +7     
  Misses        506      506              
  Partials        7        7              

Impacted Files	Coverage Δ
...c/services/workbench/explorer/folderTreeService.ts	99.46% <100.00%> (+0.02%)	⬆️

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[Zaoei]

+1

[mortalYoung]

+1