Blueprints: Use playground.documentRoot instead of hardcoding /wordpress path

[sejas]

Proposed changes

• Use playground.documentRoot from playground to avoid hardcoded paths.
• Fix documentRoot getter in base-php.

[adamziel]

You could get it inside the function like await playground.documentRoot

[sejas]

@adamziel , Great idea!, I've changed the code to grab the documentRoot from the playground variable.
I've also found a bug with the documentRoot getter. It returned the absoluteUrl instead of the documentRoot value.

[adamziel]

Great spot and great fix @sejas!