feat: Elbow arrow segment fixing & positioning (#8952)

Co-authored-by: dwelle <5153846+dwelle@users.noreply.github.com>
Co-authored-by: David Luzar <5153846+dwelle@users.noreply.github.com>

packages/excalidraw/tests/helpers/api.ts

@@ -11,6 +11,7 @@ import type {
   ExcalidrawMagicFrameElement,
   ExcalidrawElbowArrowElement,
   ExcalidrawArrowElement,
+  FixedSegment,
 } from "../../element/types";
 import { newElement, newTextElement, newLinearElement } from "../../element";
 import { DEFAULT_VERTICAL_ALIGN, ROUNDNESS } from "../../constants";
@@ -197,6 +198,7 @@ export class API {
       ? ExcalidrawArrowElement["endArrowhead"] | ExcalidrawElbowArrowElement["endArrowhead"]
       : never;
     elbowed?: boolean;
+    fixedSegments?: FixedSegment[] | null;
   }): T extends "arrow" | "line"
     ? ExcalidrawLinearElement
     : T extends "freedraw"