Stop using custom getLineForOffset

[planarvoid]

Fix

There is an issue where there is a multiline text element before a placeholder. The custom method that was calculating line for offset doesn't take that into account. I've replaced it with the default getLineForOffset and it seems to work well now.

In addition to this I've also made some of the functions in the PlaceholderManager suspended to improve performance and allow async computation

Test

1. Enable placeholders and add a multiline text followed by a placeholder to the Example field
2. Run the app
3. Notice the placeholder is drawn correctly

Review

@danilo04

Make sure strings will be translated:

• If there are new strings that have to be translated, I have added them to the client's strings.xml as a part of the integration PR.

[danilo04]

This works as expected @planarvoid. Thank you for fixing the bug and also adding support to prefetch the views concurrently. I was thinking about how to do this too but were a step ahead 🎉 !!