Refactor gameplay menus into owned scenes

ui/menus/MenuLayout.gd

@@ -0,0 +1,27 @@
+extends RefCounted
+
+const HEADER_GAP: float = 16.0
+const BOTTOM_MARGIN: float = 28.0
+
+
+static func grid_band(header_bottom: float, panel_height: float) -> Vector2:
+	var half: float = panel_height * 0.5
+	if half <= 0.0:
+		half = 640.0
+	return Vector2(header_bottom + HEADER_GAP - half, half - BOTTOM_MARGIN)
+
+
+static func grid_row_top(row: int, rows: int, row_height: float, band: Vector2,
+		natural_pitch: float) -> float:
+	var pitch: float = natural_pitch
+	if rows > 1:
+		pitch = minf(pitch, (band.y - band.x - row_height) / float(rows - 1))
+	return band.x + maxf(pitch, row_height) * float(row)
+
+
+static func place_entry(node: Control, cx: float, top: float, half: float,
+		height: float) -> void:
+	node.offset_left = cx - half
+	node.offset_right = cx + half
+	node.offset_top = top
+	node.offset_bottom = top + height