Feature Request: Update the extension's default prehiding script to hide the body

[ericmatisoff]

Expected Behaviour

The prehiding script functionality would match the precedent set by Target and Launch previously, which was to prehide the full tag.

Actual Behaviour

The prehiding script that is available via the Web SDK extension hides a custom personalization-container class which would need to be added to each element that will be personalized. If a customer did not know this change was made in the prehiding script, then they would see content flicker.

Reproduce Scenario (including but not limited to)

Steps to Reproduce

Platform and Version

Sample Code that illustrates the problem

Logs taken while reproducing problem

[jfkhoury]

I will create a JIRA ticket for this task. Thank you @ericmatisoff !