Improve bundling of web-viewer package

[jprochazk]

What

It turns out that the following issue is actually two different memory leaks in a trench coat:

• Viewer instances don't release memory when cell output is cleared #6642
  1. Module memory leaks on every execution of widget manzt/anywidget#613
  2. Memory leak when repeatedly instantiating a WASM module rustwasm/wasm-bindgen#3130

This PR addresses the 2nd one, by changing the way we output and bundle the rerun-io/web-viewer package:

• We use the new URL("./local_file.js", import.meta.url) pattern to resolve the .wasm file's URL at bundle time, and fetch it at runtime. (Side note: we can use this to expose progress tracking for Slow loading without indicator radames/gradio-rerun-viewer#5)
  • This understood by all major bundlers as "include local_file.js in the import graph as if it was loaded lazily, and return its final URL"
    • The only exception is esbuild: URL assets bundling evanw/esbuild#795
• After building the Wasm binary and running wasm-bindgen, the output is further processed to ensure that the top-level globals (such as the leak-causing heap Memory leak when repeatedly instantiating a WASM module rustwasm/wasm-bindgen#3130) are not actually global, and instead can be instantiated once per Wasm instance.
• The Wasm is loaded and compiled only once, and then instantiated once for every viewer.

To support usage in rerun_notebook and other environments which do not support the new URL pattern, the index.js, re_viewer.js, and re_viewer_bg.wasm files are concatenated into a single inlined.js file.

Checklist

• I have read and agree to Contributor Guide and the Code of Conduct
• I've included a screenshot or gif (if applicable)
• I have tested the web demo (if applicable):
  • Using examples from latest main build: rerun.io/viewer
  • Using full set of examples from nightly build: rerun.io/viewer
• The PR title and labels are set such as to maximize their usefulness for the next release's CHANGELOG
• If applicable, add a new check to the release checklist!

• PR Build Summary
• Recent benchmark results
• Wasm size tracking

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