Extract scene functions to their respective modules (#208)

- Also, extract utilities into utils module -- capitalizeString, getDateTime, isInputLike

src/scene/comparisons.ts

@@ -0,0 +1,38 @@
+import { ExcalidrawElement } from "../element/types";
+import { hitTest } from "../element/collision";
+
+export const hasBackground = (elements: ExcalidrawElement[]) =>
+  elements.some(
+    element =>
+      element.isSelected &&
+      (element.type === "rectangle" ||
+        element.type === "ellipse" ||
+        element.type === "diamond")
+  );
+
+export const hasStroke = (elements: ExcalidrawElement[]) =>
+  elements.some(
+    element =>
+      element.isSelected &&
+      (element.type === "rectangle" ||
+        element.type === "ellipse" ||
+        element.type === "diamond" ||
+        element.type === "arrow")
+  );
+
+export function getElementAtPosition(
+  elements: ExcalidrawElement[],
+  x: number,
+  y: number
+) {
+  let hitElement = null;
+  // We need to to hit testing from front (end of the array) to back (beginning of the array)
+  for (let i = elements.length - 1; i >= 0; --i) {
+    if (hitTest(elements[i], x, y)) {
+      hitElement = elements[i];
+      break;
+    }
+  }
+
+  return hitElement;
+}