fix(ContentNavigator): added name checking for duplicates on drag and drop

[kpatl1]

Summary:

I implemented error handling for drag-and-drop file operations to the SAS Server by adding a try-catch block to RestServerAdapter.moveItem(). The Viya server's updateFileOrDirectoryOnSystem API already validates for duplicate file names by default and returns an error if a file with the same name exists at the destination. The try-catch properly catches these server errors and returns undefined, allowing the UI to display an error message to the user. This fix makes RestServerAdapter consistent with the error handling patterns in RestContentAdapter and ItcServerAdapter, and relies on server-side validation as the single source of truth rather than unreliable client-side checks.

Testing:
Made a new file with the same name as one within a folder on a SAS Server. Then, I dragged the root file into the folder and it prevented me from moving it.

Fixes #1578

TODOs:

• Add any supporting documentation and (optionally) update CHANGELOG.md

[scnwwu]

I think the check should NOT be done by client. Client side check is not reliable as it's async. The file system on server may changed after your getChildren call. The server should already report error for this situation. The client just needs to display the error to user. It's not limited to name collision but whatever errors failed the operation.

As #1578 mentioned, the SAS Content pane already report error.
The UI is shared:
https://github.com/sassoftware/vscode-sas-extension/blob/main/client/src/components/ContentNavigator/ContentDataProvider.ts#L707

Both RestContentAdapter and ItcServerAdapter return falsy on error.
https://github.com/sassoftware/vscode-sas-extension/blob/main/client/src/connection/rest/RestContentAdapter.ts#L225
https://github.com/sassoftware/vscode-sas-extension/blob/main/client/src/connection/itc/ItcServerAdapter.ts#L300

So I guess RestServerAdapter should do similar.
https://github.com/sassoftware/vscode-sas-extension/blob/main/client/src/connection/rest/RestServerAdapter.ts#L450

[kpatl1]

That makes more sense. I have added the changes in to catch the error from the server side.

[Zhirong2022]

Error message pops for duplicates on drag and drop.