Add support for Alternative Input.

[pixelzoom]

Related to #160 ... @arouinfar suggest this if we proceed with PhET-iO instrumentation, then we should consider adding support for alternative input. This sim has pickers, radio buttons, accordion boxes, and 1 combo box. There are no custom UI components or draggables. So instrumentation should be mostly a matter of deciding on focus order. (Although there may be some gotchas in the Game screen, due to its highly-dynamic implementation.)

@kathy-phet FYI.

[pixelzoom]

In the above commit, I turned on alternative input and added a basic pdomOrder (everything in the play area). Next step is to design the pdomOrder.

[pixelzoom]

At 10/10/24 iteration planning meeting, this work was put on hold.

[pixelzoom]

In the above commit, I turned alt input off for the 1.3 release, which does not include alt input -- see #154.

To turn it back on, add "supportsInteractiveDescription": true, to package.json, then run grunt update.