fix issue with finding required node handles

[alanrenmsft]

This PR fixes #microsoft/azuredatastudio#14229

when the elements parameter have leaf nodes then parent nodes, this method won't work and instead of only returning the parent node, it will also returned the leaf nodes. for example, the elements contains: '1/2' (2 is a child of 1) and '1', instead of returning '1' it will return both nodes.

[alanrenmsft]

@weinand could you please take a look?

[alexr00]

@alanrenmsft is there a way I can repro the issue with VS Code?

[alanrenmsft]

@alexr00 I created an extension to reproduce the issue: https://github.com/alanrenmsft/test_tree

1. you can find the vsix test-tree-0.0.6.vsix in the repo and download it.
2. launch your local vscode dev instance and install the vsix and reload the dev instance
3. after it is loaded, you will see a view under File Explorer 'MY TREE VIEW' and make sure you expand all the nodes under it
   
4. now make sure Extension host is attached and open the file: src\vs\workbench\api\common\extHostTreeViews.ts and set breakpoint at the first line of getHandlesToRefresh method
5. Run the command "Refresh Test Tree" from command palette, you can ignore the first hit of the breakpoint and the second hit, you should see there are 2 items in the elements parameter. (the command will first refreshing node at level 4 and then refresh node at level 4 and node at level 2)
6. put a breakpoint at the end of the method and observe the value being returned.
   

expected: it should only return the node at level 2, but instead it is returning both nodes.
7. let it continue execution and you will see:

you can apply my changes locally and test it again, it should fix the problem.

[alexr00]

With your change, I'm not sure we need this part anymore:

https://github.com/alanrenmsft/vscode/blob/4499290f09b1e879958dab21bd1f4bc9521655b9/src/vs/workbench/api/common/extHostTreeViews.ts#L517-L518

[alexr00]

Very good change. Thank you for the detailed steps and sample to repro with!