[doc] Update "Get Started" page for ORT web

[fs-eire]

Description

This PR re-arranges documentation of ORT web.

Current doc: https://onnxruntime.ai/docs/
Change preview: https://fs-eire.github.io/onnxruntime/docs/

• split Doc -> Get Started -> JavaScript from single page into multiple pages, to make it easier to split from web, node and react-native
• remove Doc -> Get Started -> with Web. The page was a few links and now they are moved to other places
• add a few contents into Doc -> Get Started -> JavaScript -> Web. Now this is the main page for ORT web doc.
• rename Tutorials -> deploy on Web to Tutorials -> Web. "deploy" is confusing as it's not the accurate term to describe the content.

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ORT web documentation work item list:

• Update Get Started page for ORT web at onnxruntime.ai ( this PR )
  • to make it easier for users to navigate
• Update Tutorials page for ORT web at onnxruntime.ai
  • The purpose of this page is unclear. It contains descriptive information and step-by-step instructions on an E2E examples. It can be a good Blog, but not good for documentation, which usually has a well-structured content.
  • The index page has duplicated contents with its child page "Build a web application with ONNX Runtime"
  • Some contents are out-of-dated.
• Update API Usage - SessionOptions on onnxruntime-inference-examples repo.
  • Add explaination and examples if necessary for all new WebGPU session options.
• Update API usage - ort.env flags on onnxruntime-inference-examples repo.
  • Add all newly introduced flags.

[guschmue]

fine with this one. I think we can/should add a section for webgpu - explaining things like io-bindings, ...