Add the ability to modify a selectKit's content with `replaceContent`
Eg.
```
api.modifySelectKit("combo-box").replaceContent(() => {
return {
id: "foo",
name: "Foo",
};
});
```
will override existing content to only include the passed object
* Use QUnit `module` instead of `discourseModule`
* Use QUnit `test` instead of `componentTest`
* Use angle-bracket syntax
* Remove jQuery usage
* Improve assertions (and actually fix some of them)
In newer Embers jQuery is removed. There is a `find` but it only returns
one element and not a jQuery selector. This patch migrates our code to a
new helper `queryAll` which allows us to remove the global.
This is where they should be as far as ember is concerned. Note this is
a huge commit and we should be really careful everything continues to
work properly.
