Remove unnecessary use of DOMContentLoaded

[aduth]

🛠 Summary of changes

Updates code which binds events to DOMContentLoaded to execute immediately.

This event is typically used to ensure that all content is present on a page before executing JavaScript, in case the script is loaded earlier than the elements it references. Packs are always loaded as the last content of every page (source), so it's not necessary to wait before referencing these elements.

This also relates to #11096 and #11126, where defer has the effect of delaying DOMContentLoaded being fired, unlike asynchronous scripts. We can offset this by not relying on the DOMContentLoaded.

The DOMContentLoaded event fires when the HTML document has been completely parsed, and all deferred scripts (<script defer src="…"> and <script type="module">) have downloaded and executed. It doesn't wait for other things like images, subframes, and async scripts to finish loading.

Reference: https://developer.mozilla.org/en-US/docs/Web/API/Document/DOMContentLoaded_event

📜 Testing Plan

Verify no regressions in affected code:

• Mock device profile on the SSN step of IdV Edit: Reverted in 509ccee
• SSN formatting and visibility toggle on SSN step of IdV
• State-specific guidance for IPP

[mitchellhenke]

Is it worth adding a lint to prevent adding DOMContentLoaded listeners?

[aduth]

For awareness, I snuck an extra change in to remove this redundant condition. querySelectorAll will always return an array, and an array is always truthy.

See: https://dorey.github.io/JavaScript-Equality-Table/#if-statement

[aduth]

Is it worth adding a lint to prevent adding DOMContentLoaded listeners?

Possibly, yeah. Based on what we discovered here with legitimate usage, I might hold off on that until we remove all existing usage.