Change imports for Node.js compatibility

[Johennes]

Fixes: #4287

This changes all imports to load .js files which seems to be the only way to make Node.js understand them.

This yarn builds and lets me run the Node.js example locally. However, tests are totally broken.

The replacements were done with the following shell script with folder imports scraped from #4373 (NB: this uses BSD sed):

while read -r file; do
    # Append .js to all imports
    sed -i '' -E 's/from "(\..*)"/from "\1.js"/' "$file"
    sed -i '' -E 's/import "(\..*)"/import "\1.js"/' "$file"

    # Fix folder imports to load index.js
    sed -i '' -E 's/\.\.js"/.\/index.js"/' "$file"
    sed -i '' -E 's/(\/algorithms)\.js"/\1\/index.js"/' "$file"
    sed -i '' -E 's/(\/channels)\.js"/\1\/index.js"/' "$file"
    sed -i '' -E 's/(\/crypto-api)\.js"/\1\/index.js"/' "$file"
    sed -i '' -E 's/(\/crypto)\.js"/\1\/index.js"/' "$file"
    sed -i '' -E 's/(\/http-api)\.js"/\1\/index.js"/' "$file"
    sed -i '' -E 's/(\/oidc)\.js"/\1\/index.js"/' "$file"
    sed -i '' -E 's/(\/store)\.js"/\1\/index.js"/' "$file"
    sed -i '' -E 's/(\/transports)\.js"/\1\/index.js"/' "$file"

    # Undo some of what we did above
    sed -i '' -E 's/(@types\/.*)\/index.js"/\1.js"/' "$file"
done < <(find src -name "*.ts")

Checklist

• Tests written for new code (and old code if feasible).
• New or updated public/exported symbols have accurate TSDoc documentation.
• Linter and other CI checks pass.
• Sign-off given on the changes (see CONTRIBUTING.md).