feat(runtime): stabilize Deno.link and Deno.linkSync (#9417)

This commit makes "Deno.link" and "Deno.linkSync" stable.

The permission required has been changed to read-write to 
ensure one cannot escape the sandbox.

cli/dts/lib.deno.ns.d.ts

@@ -265,6 +265,27 @@ declare namespace Deno {
    */
   export function cwd(): string;
 
+  /**
+   * Synchronously creates `newpath` as a hard link to `oldpath`.
+   *
+   * ```ts
+   * Deno.linkSync("old/name", "new/name");
+   * ```
+   *
+   * Requires `allow-read` and `allow-write` permissions. */
+  export function linkSync(oldpath: string, newpath: string): void;
+
+  /**
+   *
+   * Creates `newpath` as a hard link to `oldpath`.
+   *
+   * ```ts
+   * await Deno.link("old/name", "new/name");
+   * ```
+   *
+   * Requires `allow-read` and `allow-write` permissions. */
+  export function link(oldpath: string, newpath: string): Promise<void>;
+
   export enum SeekMode {
     Start = 0,
     Current = 1,