Merge button tweaks

[Huddie]

So seems like we’re sticking with #2051 for the merge button which looks awesome! Regardless I was thinking:

1. Redesign merge button in landscape (Resizes properly but it looks very (unnecessarily) wide.
2. When you tap the down chevron on the merge button it triggers a UIAlertController. Context menu fits better since a in-app action occurs which is context menus main use at the moment
3. Sometimes pull requests have comments, scrolling all the way to the bottom isn’t a big deal but if there was a floating “quick merge” button that could be cool possibly. Maybe add it in the manager button context menu. - still would need the main merge button at the bottom letting you know no conflicts and checks that passed/failed..etc but assuming all checks passed and no conflict it should show as an option in the manager button

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