Omnibar position option

[0nko]

Task/Issue URL:

Description

This is a feature branch for the omnibar position project.

[0nko]

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[0nko]

The big issue is that when the omnibar is at the bottom we are over the web content, and not properly pushing it to the top. That makes it so any content at the bottom of the viewport is behind the omnibar.

@malmstein Thanks for the review. I will fix this in a separate PR. The rest of the comments should be addressed now.

I added steps for testing different scenarios in the PR description.

[malmstein]

• #4885 : 4 dependent PRs (#4886 , #4940 , #4941 and 1 other) 👈
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[0nko]

@malmstein I’ve addressed your comments but I also had to make some additional changes:

• I changed the way we check if the feature flag is enabled. There are many places that check the position value. To avoid adding a feature flag check everywhere, I added a plugin that checks on process start and modifies the data store.
• I updated the JS that checks the scrollability of a website and it’s now able to correctly determine that theguardian.com and similar sites have a non-scrollable elements at the front
• I found that the omnibar is scrollable when showing autocomplete (a behavior that is present in production) and I made it fixed

[0nko]

@malmstein I’ve updated the test instructions to include tests of the feature flag, as well.