add first draft of glossary

GLOSSARY.md

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+TODO dvdsk copy latest from notes
+
+These are some terms and structures frequently used throughout the zed codebase. This is a best effort list. PR's are very welcome.
+
+Questions:
+
+- Can we generate this list form doc comments throughout zed?
+
+## GPUI
+
+- `Context`: A wrapper around the App struct with specialized behavior for a specific Entity
+- `App`: A singleton which holds the full application state including all the entities.
+- `AsyncApp`:
+- `Window`:
+- `Task`:
+- `Executor`:
+  - both background and foreground
+- `Entity`: A strong, well-typed reference to a struct which is managed by gpui. Effectively a pointer into the Context.
+- `Global`: A singleton type which has only one value
+- `Event`: A datatype which can be send by an Entity to subscribers
+- `Action`: An event that represents a user's keyboard input that can be handled by listerners
+  Example: `file finder: toggle`
+- `Subscription`: An event handler that is used to react to the changes of state in the application.
+  1. Emitted event handling
+  2. Observing {new,release,on notify} of an entity
+- `Focus`: The place where keystrokes are handled first
+- `Element`: An type that can be rendered
+- `AnyElement`: A type erased version of an Element
+- `element expression`: An expression that builds an element tree, example:
+```
+h_flex()
+    .id(text[i])
+    .relative()
+    .when(selected, |this| {
+        this.child(
+            div()
+                .h_4()
+                .absolute()
+                etc etc
+```
+
+## Zed
+
+- `Workspace`: The root of the window <TODO add image>
+- `Buffer`: The in memory representation of a 'file' together with relevant data such as syntax trees, git status and diagnostics.
+- `Picker`: A model showing a list of items. When an item is selected you can confirm the item and then something happens. <TODO add image>
+- `PickerDelegate`: A trait used to specialize behavior for a Picker
+- `Modal`: todo! <TODO add image>
+- `Project`: todo! <TODO add image>
+- `Stores`: todo!
+
+## Collab
+
+- `Upstream client`: The zed client which has shared their workspace
+- `Downstream client`: The zed client joining a shared workspace
+
+## Debugger
+
+- `DapStore`: Is an entity that manages debugger sessions
+- `debugger::Session`: Is an entity that manages the lifecycle of a debug session and communication with DAPS
+- `BreakpointStore`: Is an entity that manages breakpoints states in local and remote instances of Zed
+- `DebugSession`: Manages a debug session's UI and running state
+- `RunningState`: Directily manages all the views of a debug session
+- `VariableList`: The variable and watch list view of a debug session
+- `Console`
+- `Terminal`
+- `BreakpointList`
+- `