feat: add dataset selector operator

[aglinxinyuan]

What changes were proposed in this PR?

This PR adds a new Dataset Selector operator that allows users to select a dataset from the property panel and output one tuple per filepath in that version. The emitted values follow Texera’s existing dataset file path format, so they can be consumed directly by downstream operators. On the frontend, this PR adds a dedicated dataset-version selector field in the property panel and wires datasetVersionPath to that custom UI.

Any related issues, documentation, discussions?

Closes #4363.

How was this PR tested?

Tested manually, and a test case was added.
The test covers the dataset selector descriptor metadata and output schema.

Was this PR authored or co-authored using generative AI tooling?

No.

[Copilot]

Pull request overview

Adds a new Dataset Selector source operator that lets users pick a dataset version in the property panel and emits one tuple per file path in that version, using Texera’s dataset path format.

Changes:

• Backend: introduce DatasetSelectorSourceOpDesc + DatasetSelectorSourceOpExec and register the operator type.
• Frontend: add a custom Formly field (datasetversionselector) to select dataset + version and bind it to datasetVersionPath.
• Tests/assets: add a basic descriptor/schema unit test and an operator icon.

Reviewed changes

Copilot reviewed 9 out of 10 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
frontend/src/assets/operator_images/DatasetSelector.png	Adds an icon for the new operator.
frontend/src/app/workspace/component/property-editor/operator-property-edit-frame/operator-property-edit-frame.component.ts	Maps datasetVersionPath to a custom Formly control type.
frontend/src/app/workspace/component/dataset-version-selector/dataset-version-selector.component.ts	Implements dataset+version selector logic and writes back datasetVersionPath.
frontend/src/app/workspace/component/dataset-version-selector/dataset-version-selector.component.html	UI for dataset and version dropdowns.
frontend/src/app/common/formly/formly-config.ts	Registers the new Formly field type datasetversionselector.
frontend/src/app/app.module.ts	Declares the new selector component.
common/workflow-operator/src/test/scala/.../DatasetSelectorSourceOpDescSpec.scala	Adds unit tests for descriptor metadata and output schema.
common/workflow-operator/src/main/scala/.../DatasetSelectorSourceOpExec.scala	Implements tuple production by resolving dataset version and listing objects.
common/workflow-operator/src/main/scala/.../DatasetSelectorSourceOpDesc.scala	Defines operator metadata + output schema (filename).
common/workflow-operator/src/main/scala/.../LogicalOp.scala	Registers DatasetSelector in the operator type list.

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