fix(inputs): ignoring input events in IE caused by placeholder changes o...

...r focus/blur on inputs with placeholders

This is my attempt at fixing #8242 as well as the extra placeholder issues with focus/blur. I'm assuming I'm missing a weird test case that still breaks somewhere, but I still think this is an improvement (it definitely is for my use cases).
If this is true then we could factor this out into a helper method:

```js
function changePlaceholder(value) {
  attrs.$set('placeholder', value);
  if (msie) {
    browserTrigger(inputElm, 'input');
  }
}
```