Fix remote mode multi-file selection via Show Local dialog (#300408)

* Initial plan

* Fix remote mode multi-file selection via Show Local dialog

Change ISimpleFileDialog.showOpenDialog to return URI[] instead of single URI.
When 'Show Local' is clicked in remote file dialog, pass through all selected
files from the native dialog instead of only taking the first result.

Co-authored-by: alexr00 <[email protected]>

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Co-authored-by: copilot-swe-agent[bot] <[email protected]>
Co-authored-by: alexr00 <[email protected]>