Fix website to work with ESM

[felixpalmer]

Currently these changes allow the website to be ran locally using yarn start, but yarn build-staging fails.

In order to publish the website, instances to import GL from '@luma.gl/constants'; will need to be removed (to be done in followup PR)

Change List

• Fix write-headings-id script
• Remove inline-webgl-constants script

[Pessimistress]

My understanding is that we won't have WebGL-specific constants in v9, therefore inline-webgl-constants can just be removed.

remove-glsl-comments should still work, though? It doesn't have any dependency on luma packages.

[felixpalmer]

@Pessimistress remove-glsl-comments was just missing from package.json