Return list of destination URIs from LocalFilesystemToGCSOperator

[yuseok89]

Related: #11323

• Return value: execute() now returns a list[str] of destination URIs for uploaded files (single file, list of files, or glob). This operator did not return a value before, so unwrap_single was not added..

• Deduplication for multi-file upload: When multiple source paths map to the same destination (e.g. src=["a.png", "a.png"] or src=["data/foo.png", "data/*"] with data/ containing only foo.png), the same URI can appear more than once. The result list is deduplicated while preserving order via dict.fromkeys.

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Test screenshot

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[bugraoz93]

Looks good, would be good to get a stamp from @shahar1 too!

[shahar1]

Great job!
Are you able to run the system tests for the related operator with the new change and attach a screenshot that they pass? Please let us know if it's an issue.
Didn't notice the screenshot, LGTM!

CC: @VladaZakharova @MaksYermak - WDYT?
If no objections are made, as both CI and system tests passed - this PR will be merged by the upcoming release on Tuesday.