Proposal: Let users type to search the dataset/file picker inside a workflow

[yangzhang75]

Body
Opening this for feedback before any work.

Summary

In the file picker inside a workflow (the "Select File" dialog on operators like CSV
File Scan), you can currently only scroll and click to find a dataset. Let users type to
filter it instead.

Motivation

When there are many datasets, scrolling to find the right one is slow. Typing a few
letters to narrow it down is much faster.

Proposed change

The dataset and version pickers are already nz-select dropdowns. Turn on ng-zorro's
built-in nzShowSearch, so typing filters the list by name. Optionally, make the file
tree (picking the file within a version) searchable too.

This is a frontend-only change — no backend work, it just filters the list already
loaded in the dialog.

Open questions

1. Should search match only the dataset name, or also the #id number
   (e.g. typing 17 finds #17 iris)? I'd lean toward matching both.
2. Should the file tree (choosing the file within a version) also be searchable, or just
   the dataset/version dropdowns for now?
3. Any concerns with client-side filtering when a dataset list gets very large?

[aglinxinyuan]

1. Matching both.
2. Just dropdowns for now.
3. It's a separate issue.

The design looks good to me. You can work on it.

[chenlica]

Agreed. This feature was suggested during a recent education program using Texera.