Add DataView dataStart definition (#2224)

Author: jafri

NOTICE

@@ -45,6 +45,7 @@ under the licensing terms detailed in LICENSE:
 * Congcong Cai <[email protected]>
 * mooooooi <[email protected]>
 * Yasushi Ando <[email protected]>
+* Syed Jafri <[email protected]>
 
 Portions of this software are derived from third-party works licensed under
 the following terms:

std/assembly/index.d.ts

@@ -1504,6 +1504,8 @@ declare class ArrayBuffer {
 declare class DataView {
   /** The `buffer` accessor property represents the `ArrayBuffer` or `SharedArrayBuffer` referenced by the `DataView` at construction time. */
   readonly buffer: ArrayBuffer;
+  /** Returns raw pointer to data storage including offset (unsafe). */
+  readonly dataStart: usize;
   /** The `byteLength` accessor property represents the length (in bytes) of this view from the start of its `ArrayBuffer` or `SharedArrayBuffer`. */
   readonly byteLength: i32;
   /** The `byteOffset` accessor property represents the offset (in bytes) of this view from the start of its `ArrayBuffer` or `SharedArrayBuffer`. */