update vitepress, fix a build crash, add a sitemap

[Fil]

• fix a crash with docs:build and figure.append / el.append
• upgrade vitepress to 1.0.0-rc.4 (https://github.com/vuejs/vitepress/blob/main/CHANGELOG.md)
• generate a sitemap at ./docs/.vitepress/dist/sitemap.xml (available with the vitepress update, see feat: sitemap generation vuejs/vitepress#2691; documentation: https://vitepress.dev/guide/sitemap-generation#sitemap-generation)

Re: the crash, I don't understand why it doesn't seem to happen in production. When I call yarn docs:build with the current main branch, I get dozens of errors:

✓ building client + server bundles...
⠹ rendering pages...TypeError: Function.prototype.apply was called on undefined, which is a undefined and not a function
    at Module.plot (file:///Users/fil/Sites/plot/docs/.vitepress/.temp/plot.c0318f47.js:5839:12)
    at Proxy.render (file:///Users/fil/Sites/plot/docs/.vitepress/.temp/PlotRender.53d19871.js:788:35)
    at renderComponentRoot (/Users/fil/Sites/plot/node_modules/@vue/runtime-core/dist/runtime-core.cjs.prod.js:399:16)
    at renderComponentSubTree (/Users/fil/Sites/plot/node_modules/@vue/server-renderer/dist/server-renderer.cjs.prod.js:440:28)
    at renderComponentVNode (/Users/fil/Sites/plot/node_modules/@vue/server-renderer/dist/server-renderer.cjs.prod.js:371:12)
    at ssrRenderComponent (/Users/fil/Sites/plot/node_modules/@vue/server-renderer/dist/server-renderer.cjs.prod.js:86:10)

plot.c0318f47.js:5839 is our figure.append(...legends, svg).

[mbostock]

This isn’t strictly necessary (we could have upgraded vitepress with just yarn upgrade and changing the yarn.lock file. But I guess since we’re using the sitemap feature added in beta.7, this is okay. The point being, 1.0.0-rc.4 is already consistent with ^1.0.0-beta.2.

[mbostock]

Looks like we’ve picked up multiple copies of rollup and vite in this upgrade. This is why I generally prefer to upgrade everything at once via yarn upgrade rather than doing it piecemeal. I’ll do that now and push to this branch.

[mbostock]

I had to downgrade Vite & Vitepress in 2511ef3 due to client-side navigation being broken. (The left nav would often scroll up to the top and reset which sections were open.)

[Fil]

issue reported upstream vuejs/vitepress#2796