Add macOS window tabs (#33334)

Closes https://github.com/zed-industries/zed/issues/14722
Closes https://github.com/zed-industries/zed/issues/4948
Closes https://github.com/zed-industries/zed/issues/7136

Follow up of https://github.com/zed-industries/zed/pull/20557 and
https://github.com/zed-industries/zed/pull/32238.

Based on the discussions in the previous PRs and the pairing session
with @ConradIrwin I've decided to rewrite it from scratch, to properly
incorporate all the requirements. The feature is opt-in, the settings is
set to false by default. Once enabled via the Zed settings, it will
behave according to the user’s system preference, without requiring a
restart — the next window opened will adopt the new behavior (similar to
Ghostty).

I’m not entirely sure if the changes to the Window class are the best
approach. I’ve tried to keep things flexible enough that other
applications built with GPUI won’t be affected (while giving them the
option to still use it), but I’d appreciate input on whether this
direction makes sense long-term.



https://github.com/user-attachments/assets/9573e094-4394-41ad-930c-5375a8204cbf

### Features
* System-aware tabbing behavior
* Respects the three system modes: Always, Never, and Fullscreen
(default on macOS)
* Changing the Zed setting does not require a restart — the next window
reflects the change
* Full theme support
    * Integrates with light and dark themes
* [One
Dark](https://github.com/user-attachments/assets/d1f55ff7-2339-4b09-9faf-d3d610ba7ca2)
* [One
Light](https://github.com/user-attachments/assets/7776e30c-2686-493e-9598-cdcd7e476ecf)
    * Supports opaque/blurred/transparent themes as best as possible
* [One Dark -
blurred](https://github.com/user-attachments/assets/c4521311-66cb-4cee-9e37-15146f6869aa)
* Dynamic layout adjustments
    * Only reserves tab bar space when tabs are actually visible
* [With
tabs](https://github.com/user-attachments/assets/3b6db943-58c5-4f55-bdf4-33d23ca7d820)
* [Without
tabs](https://github.com/user-attachments/assets/2d175959-5efc-4e4f-a15c-0108925c582e)
* VS Code compatibility
* Supports the `window.nativeTabs` setting in the VS Code settings
importer
* Command palette integration
    * Adds commands for managing tabs to the command palette
* These can be assigned to keyboard shortcuts as well, but didn't add
defaults as to not reserve precious default key combinations

Happy to pair again if things can be improved codewise, or if
explanations are necessary for certain choices!



Release Notes:
* Added support for native macOS window tabbing. When you set
`"use_system_window_tabs": true`, Zed will merge windows in the same was
as macOS: by default this happens only when full screened, but you can
adjust your macOS settings to have this happen on all windows.

---------

Co-authored-by: Conrad Irwin <conrad.irwin@gmail.com>

docs/src/configuring-zed.md

@@ -1421,6 +1421,16 @@ or
 
 Each option controls displaying of a particular toolbar element. If all elements are hidden, the editor toolbar is not displayed.
 
+## Use System Tabs
+
+- Description: Whether to allow windows to tab together based on the user’s tabbing preference (macOS only).
+- Setting: `use_system_window_tabs`
+- Default: `false`
+
+**Options**
+
+This setting enables integration with macOS’s native window tabbing feature. When set to `true`, Zed windows can be grouped together as tabs in a single macOS window, following the system-wide tabbing preferences set by the user (such as "Always", "In Full Screen", or "Never"). This setting is only available on macOS.
+
 ## Enable Language Server
 
 - Description: Whether or not to use language servers to provide code intelligence.