👀 Workspace UI

## Overview

The workspace is the UI used within a project around the editor view (#36). We need to provide the UI laid out in our [this concept](https://www.figma.com/proto/qj6raZbQsZpGO0NAVi4qsv/CodeEdit-Concept?node-id=1%3A870) that includes the following tasks.

Please refer to our [documentation](https://github.com/CodeEditApp/CodeEdit/wiki/Workspace-Windowing-&-Layout-Strategy) around how we think our Workspace UI should work and behave.

## Tasks

- [ ] #347
- [x] #142
- [ ] #1523
- [x] #349
- [x] #37
- [x] #350
- [x] #38
- [x] #338
- [ ] #479
- [x] #438
- [ ] #42
- [x] #635

## Additional context

- [VSCode UI - Workbench](https://code.visualstudio.com/docs/getstarted/userinterface)

リンクされたFigmaのworkspaceコンセプトとWorkspace Windowing & Layout Strategyのドキュメントから始め、その後、未チェックのタスクissue（#347、#1523、#479、#42）を確認します。workspaceのエディタービュー周辺のUIがコンセプトと一致し、記載されたworkspaceタスクが完了していれば完了です。

索引モデルが issue の本文から書いたものです。