feat(components): [transfer] export transfer source data & method

[warmthsea]

Finish: https://github.com/element-plus/element-plus/discussions/18152

Playground Demo

[github-actions[bot]]

[github-actions[bot]]

🧪 Playground Preview: https://element-plus.run/?pr=18162 Please comment the example via this playground if needed.

[pkg-pr-new[bot]]

Open in StackBlitz

pnpm add https://pkg.pr.new/element-plus/element-plus@18162

commit: 47c149a

[warmthsea]

Open in Stackblitz

pnpm add https://pkg.pr.new/element-plus/element-plus@18162

commit: 6bb2ecc

@8502596 If you want to use it now, you can install it with this command. This PR will also make some improvements to the el-transfer component.

[github-actions[bot]]

@warmthsea This PR has conflicts, please resolve them.

[btea]

The version label needs to be updated.

[warmthsea]

The version label needs to be updated.

updated.