Filechooser: hide file browser by default in save dialogs

## Problem

99% of users will just save the file to their Documents folder or to a bookmarked location.
If a user wants to save a file, any file, they are met with a worse version of the normal file browser. This is visual bloat and confusing for users, since it brings the user's entire app-workflow to a grinding halt as it opens something that resembles a seperate app and likely obscures the entire underlying window.
~~There is also the issue of the file saving dialogue not feeling completely native, since it is retrofitted on to the normal gtk.filechooser-dialogue afaik~~ Edit: looking at the new FileChooser tells me otherwise, but it also demonstrates how the filechooser looks similar to the actual Files app but uses an entirely different sidebar

## Proposal

Elementary OS should have it's own file saving dialogue box, which has a name entry box at the top, a drop down with the users default and bookmarked locations. MacOS handles this in this exact way (at least it used to)

This should also solve the issue of not having a fully-native filechooser dialogue

## Prior Art

How macOS 10.4 handled it is a really good example.
Default size:
Expanded size:

I'd love to hear what elementary/us think!