Start on a database-backed prompt library (#12468)

Using the file system as a database seems like it's easy, but it's
actually a real pain. I'd like to use LMDB to store the prompts locally
so we have more control. We can always add an export option, but I want
the source of truth to be somewhere other than the file system.

So far, I have a PromptStore which is global to the application and can
be initialized on startup. Then there's a `PromptLibrary` which is
intended to be the root of a new kind of Zed window. I haven't actually
seen pixels yet, but I've sketched out the basics needed to create a new
prompt, save, etc.

Still lots to figure out but the foundations of being backed by a DB and
rendering in an independent window are in place.

/cc @iamnbutler @as-cii 

Release Notes:

- N/A

---------

Co-authored-by: Antonio Scandurra <me@as-cii.com>

crates/project_panel/src/project_panel.rs

@@ -12,9 +12,10 @@ use git::repository::GitFileStatus;
 use gpui::{
     actions, anchored, deferred, div, impl_actions, px, uniform_list, Action, AnyElement,
     AppContext, AssetSource, AsyncWindowContext, ClipboardItem, DismissEvent, Div, EventEmitter,
-    FocusHandle, FocusableView, InteractiveElement, KeyContext, Model, MouseButton, MouseDownEvent,
-    ParentElement, Pixels, Point, PromptLevel, Render, Stateful, Styled, Subscription, Task,
-    UniformListScrollHandle, View, ViewContext, VisualContext as _, WeakView, WindowContext,
+    FocusHandle, FocusableView, InteractiveElement, KeyContext, ListSizingBehavior, Model,
+    MouseButton, MouseDownEvent, ParentElement, Pixels, Point, PromptLevel, Render, Stateful,
+    Styled, Subscription, Task, UniformListScrollHandle, View, ViewContext, VisualContext as _,
+    WeakView, WindowContext,
 };
 use menu::{Confirm, SelectFirst, SelectLast, SelectNext, SelectPrev};
 use project::{Entry, EntryKind, Fs, Project, ProjectEntryId, ProjectPath, Worktree, WorktreeId};
@@ -2217,6 +2218,7 @@ impl Render for ProjectPanel {
                         },
                     )
                     .size_full()
+                    .with_sizing_behavior(ListSizingBehavior::Infer)
                     .track_scroll(self.scroll_handle.clone()),
                 )
                 .children(self.context_menu.as_ref().map(|(menu, position, _)| {