macos: render a terminal in the slide window

macos/Sources/Features/SlideTerminal/SlideTerminalPosition.swift

@@ -0,0 +1,41 @@
+import Cocoa
+
+enum SlideTerminalPosition {
+    case top
+
+    /// Set the initial state for a window for animating out of this position.
+    func setInitial(in window: NSWindow, on screen: NSScreen) {
+        // We always start invisible
+        window.alphaValue = 0
+
+        // Position depends
+        switch (self) {
+        case .top:
+            window.setFrame(.init(
+                origin: .init(
+                    x: 0,
+                    y: screen.frame.maxY),
+                size: .init(
+                    width: screen.frame.width,
+                    height: window.frame.height)
+            ), display: false)
+        }
+    }
+
+    /// Set the final state for a window in this position.
+    func setFinal(in window: NSWindow, on screen: NSScreen) {
+        // We always end visible
+        window.alphaValue = 1
+
+        // Position depends
+        switch (self) {
+        case .top:
+            window.setFrame(.init(
+                origin: .init(
+                    x: window.frame.origin.x,
+                    y: screen.visibleFrame.maxY - window.frame.height),
+                size: window.frame.size
+            ), display: true)
+        }
+    }
+}