Improve handling of validation errors for enqueued scripts
Improve handling of validation errors for enqueued scripts

* Eliminate enqueued_script validation error in favor of merging sources into invalid_element errors
* Add source information for inline scripts attached to enqueued scripts.
* Account for enqueueing script bundles (where src is false).
* Capture inline script contents in validation errors. Fixes #1031.

ampproject/amp-toolbox-php,ampproject/amp-toolbox-php