This fixes the crash users have been reporting with the theme selector

For whatever reason, the optimizations of panes and workspace have
caused the terminal to notify less often then it should. This PR fixes
that oversight.

The files will still get created if the user opens their settings and
saves, otherwise everything will transparently work

Release Notes:

- Fixed an issue where a missing settings file would cause a hang on
startup
([#1590](https://github.com/zed-industries/community/issues/1590)).

This code is intended to be removed at a later date.

Release Notes:

- N/A

Release Notes:

* Fixed the behavior of panel buttons when their panel is open. Show the
key binding for closing the containing dock (preview only).
* Improved the styling of zoomed panels and panes, giving them a
stronger border, and color the zoom button with an "active" style
(preview only).
* Improved the stability of panels' zoom state. Close their dock instead
of resetting their zoom state when dismissing panels to reveal other
items (preview only).

Use new theme file structure
```
themes/
  [theme_name]
    [theme_name]-common.ts
    [theme_name]-light.ts
    [theme_name]-dark.ts
    LICENSE
```

Release Notes: 
- N/A

This PR updates the dock key bindings according to the following model:

There are three bits: 
Visible: Opened / closed.
Focus: Panel focused / center focused.
Zoom: Zoomed / Not zoomed.

Each of these variables is 'sticky' in that they won't effect each other
unless they need to. 'Zooming' a panel conceptually merges the visible
and focus bits.

cmd-shift-j/b/r have all been removed.

cmd-j/b/r have been updated to mean 'toggle visibility of a certain
dock', firing them should *always* reveal the panel to you (where you
last left it), or hide it, without moving focus (unless the focused
element is invisible). This means that, when the terminal panel is
zoomed, cmd-j has the same effect as ctrl-`

ctrl-` and cmd-shift-e now toggle a panel's focus, without updating the
zoom state of a panel. Toggling the focus of a zoomed panel causes it to
automatically hide itself, without losing the zoom bit.

When focused or made visible, panels which cannot be zoomed
automatically unzoom everything else so as to preserve user intent of
'show me this panel' and 'everything stays where it is if I don't take
an action'

Release Notes:

- cmd-shift-j/b/r have been removed.  (preview only)
- cmd-j/b/r unconditionally show or hide their associated dock,
respecting zoom settings. (preview only)
- ctrl-` and cmd-shift-e now retain zoom state. (preview only)
- Fixed a bug where terminal dock tab would always be in the active
state (preview only)
- Fixed a bug where terminals would not always open in the terminal
panel
- Changed the look of zoomed panels to fill more of the screen (preview
only)

co-authored-by: max <max@zed.dev>

co-authored-by: max <max@zed.dev>

co-authored-by: max <max@zed.dev>

Rather than assuming a specific family exists, try a set of specific
names and if they fail, just grab any old font that the system reports
as existing

Closes
https://linear.app/zed-industries/issue/Z-445/thread-main-panicked-at-called-resultunwrap-on-an-err-value-could-not

Release Notes:

* Fixed crash that could happen if system did not have a specific
fallback font

co-authored-by: max <max@zed.dev>

Add release note lines here:

N/A

co-authored-by: max <max@zed.dev>

co-authored-by: max <max@zed.dev>

Rather than assuming a specific family exists, try a set of specific
names and if they fail, just grab any old font that the system reports
as existing

Co-Authored-By: Nathan Sobo <nathan@zed.dev>

This pull request simplifies the `Pane` struct by replacing methods like
`Pane::add_item` that would previously take a `&mut Workspace` with
methods that take a `&mut self`. When access to the workspace is needed,
we now either emit an event from the `Pane` or directly move the method
to the `Workspace` struct.