Refactor/update combobox

[cal-smith]

It's been left alone for a while, and it definitely could use some love

[sjbeatle]

There are numerous DAP violations (especially for the complex integration "with reactive forms"

I don't think it's currently following proper accessibility guidelines for comboboxes:

• DAP Details
• WAI-ARIA Authoring Practices for Combobox
• There's a typo:
  https://github.com/IBM/carbon-components-angular/blob/3eec9ffcda917c55c8c95e17cdb26483e0a4bd6e/src/combobox/combobox.component.ts#L93

[cal-smith]

Thanks for doing that digging @sjbeatle!

[sjbeatle]

Thanks for doing that digging @sjbeatle!

My pleasure!! I plan to contribute more but time has proven a scarce resource as of late 😕