[help_editor] fix preview button

[maltheism]

Brief summary of changes

This PR updates the position of the preview dialogue when clicking on the preview button of the help editor. It also correctly sources the sweetalert library from htdocs/vendor because help_editor_helper.js is vanilla javascript and isn't compiled with webpack (needed for using import).

Testing instructions (if applicable)

1. Checkout PR
2. Visit the help_editor module
3. click on bmi in the table (example rasinbread)
4. Click the preview button.

Link(s) to related issue(s)

• Resolves #6968

[shonibare]

Here is the screenshot of the result. The preview button now works @ridz1208

[regisoc]

Works too

[cmadjar]

@shonibare @regisoc if this is approved, can you approve the PR? Thanks!

[cmadjar]

@driusan PR was approved by Regis. In your code for final review.