[Refactor] Move text_to_image.py from offline_inference/qwen_image to offline_inference/text_to_image

[divyanshsinghvi]

PLEASE FILL IN THE PR DESCRIPTION HERE ENSURING ALL CHECKLIST ITEMS (AT THE BOTTOM) HAVE BEEN CONSIDERED.

Purpose

Refactor text_to_image.py to allow it to work with other diffusion models.

Test Plan

python examples/offline_inference/text_to_image/text_to_image.py --model AIDC-AI/Ovis-Image-7B --prompt "A man skiing from a roller coaster in a desert" --height 128 --width 128 --num_inference_steps 10

Test Result

---

Essential Elements of an Effective PR Description Checklist

• The purpose of the PR, such as "Fix some issue (link existing issues this PR will resolve)".
• The test plan, such as providing test command.
• The test results, such as pasting the results comparison before and after, or e2e results
• (Optional) The necessary documentation update, such as updating supported_models.md and examples for a new model.
• (Optional) Release notes update. If your change is user facing, please update the release notes draft.

BEFORE SUBMITTING, PLEASE READ https://github.com/vllm-project/vllm-omni/blob/main/CONTRIBUTING.md (anything written below this line will be removed by GitHub Actions)

[hsliuustc0106]

I think this PR is no longer necessary with #274 merged