Fix js/chat example

[joncamp]

The chat example is broken currently, as noted in #431. TLDR: Update Onnxruntime-web in chat sample to be v1.20.1

There are two symptoms that are displayed in the console. One is a failure to initialize the session, leading to TypeError: Cannot read properties of undefined (reading 'run'). That error is somewhat ambiguous. However, running under a debugger we see a more descriptive error:

Error: no available backend found. ERR: [webgpu] TypeError: r.requestAdapterInfo is not a function
    at On (ort.webgpu.min.js:6:1623)
    at async e.create (ort.webgpu.min.js:6:18113)
    at async LLM.load (llm.js:113:1)
    at async Init (main.js:256:1)

Per https://issues.chromium.org/issues/346321149, requestAdapterInfo was deprecated. gyagp/onnxruntime@2a70ffd is the associated PR into onnxruntime making the update.

This change only updates the chat sample. Other samples (ort-whisper, quick-start_onnxruntime-web-bundler, sd-turbo, and segment-anything) all use even older onnxruntime-web packages. For sd-turbo, PR #498 submitted an equivalent change for a different issue. Consider updating all of the onnxruntime-web packages.