Issue #3548040: Embed snippet should use absolute link for resizer url

Problem

he H5P embed snippet includes a link to the h5p-resizer.js script. This link needs to be an absolute URL (i.e., it should include the protocol and domain) because H5Ps are often embedded on other websites.

Changes

Closes #3548040

Tests

• Create an H5P item
• Ensure the "Embed button" configuration is set to show either globally or for this item
• Click the <> Embed button to show the Embed modal dialog
• Copy the Embed snippet
• Ideally, paste the embed snippet in another website and ensure the resizer JS file loads and works to resize the iframe so it fits the content.
• Also, paste the snippet text in an editor
• Note that the resizer JS URL contains the protocol and domain.