Welcome Window Improvements

[austincondiff]

Description

This PR makes the following improvements to the Welcome window:

• Changed window style to be consistent with Xcode's
• Made welcome action symbols a bit smaller
• Fixed bug where removing recents via context menu was removing wrong items

Note: There are several issues with the .plain window style so we had to make the following workarounds:

• Focusing list by default so it is highlighted
• Handling keyboard navigation manually

Checklist

• I read and understood the contributing guide as well as the code of conduct
• The issues this PR addresses are related to each other
• My changes generate no new warnings
• My code builds and runs on my machine
• My changes are all related to the related issue above
• I documented my code

Screenshots

Before

After

[austincondiff]

Note to self: I need to handle cmd W because this no longer closes the window, which is why tests fail. I also will need a better way to identify the welcome window to apply the shadow because sometimes it is not getting applied to the correct window.

There is also an issue when opening a file or folder and it adds a new item to the recents list, where the list contents begin above the window’s top edge resulting in the top of the new item being cut off. It is fixed when scrolling at all. I assume the scroll view is miscalculating to scroll top position.