Refactor expression types

[andresmgot]

What happened:

The types defined in expressions.ts does not match reality. For example, where, reduce and groupBy elements of a ADX query, are marked as QueryEditorArrayExpression which is always an array of QueryEditorExpression, while the real type are QueryEditorOperatorExpression or QueryEditorReduceExpression or QueryEditorGroupByExpression, requiring some manual casting in some places.

The goal of this issue is to properly define these types so the casting (as) is not necessary.

What you expected to happen:

How to reproduce it (as minimally and precisely as possible):

Screenshots

Anything else we need to know?:

Environment:

• Grafana version:
• Plugin version: 4.1.6
• OS Grafana is installed on:
• User OS & Browser:
• Others: