Reset warming/cooling indexing when settled

[zepumph]

In addition to reset on endDrag, it is nice to reset this when we settle things out. I accidentally already committed half of this over in https://github.com/phetsims/friction/issues/253:

https://github.com/phetsims/friction/blob/53827d7d2e61143852ec84660040a16b8f4f2c9a/js/friction/view/TemperatureDecreasingAlerter.js#L114-L120

I'll complete it here.

[zepumph]

Buggy behavior before this work:

• Start dragging, hear the progression of warming alerts warmer -> hotter jiggling fast -> faster
• Stop moving the book, but keep dragging. hear the progression of cooling alerts, all the way to "even cooler. . . even less"
• Wait for the temperature to be settled and alert that it is settled, don't end your drag.
• Start warming again, it will start with "even hotter" (the last one). Same with cooling.

Now once settled, it will reset and start with "warmer" again, and basic "cooler" alerts too. This is pretty much just for mouse because you can't keep a drag really like that with a keyboard (keeping a key pressed). Though I'm sure it's possible.

Closing