Feat/model backed ui (#1145)

This is an initial PR for a new model-driven UI where extensions can provide definitions of the components & how they're laid out using Containers.
#1140, #1141, #1142, #1143 and #1144 are all tracking additional work needed to improve the initial implementation and fix some issues with the implementation.

Features:
- Supports defining a FlexContainer that maps to a flexbox-based layout.
- Supports creating a card component, which is a key-value pair based control that will lay out simple information to a user. Eventually this will have an optional set of actions associated with it.
- Has a sample project which shows how to use the API and was used for verification

samples/sqlservices/src/media/insights.svg

@@ -0,0 +1 @@
+<svg id="Layer_1" data-name="Layer 1" xmlns="http://www.w3.org/2000/svg" viewBox="0 0 16 16"><defs><style>.cls-1{fill:#212121;}</style></defs><title>insights</title><path class="cls-1" d="M15,4V8H14V5.71L9.49,10.2l-2-2L2,13.71V14H15v1H1V1H2V12.29L7.49,6.8l2,2L13.28,5H11V4Z"/></svg>

samples/sqlservices/src/media/insights_inverse.svg

@@ -0,0 +1 @@
+<svg id="Layer_1" data-name="Layer 1" xmlns="http://www.w3.org/2000/svg" viewBox="0 0 16 16"><defs><style>.cls-1{fill:#fff;}</style></defs><title>insights_inverse</title><path class="cls-1" d="M15,4V8H14V5.71L9.49,10.2l-2-2L2,13.71V14H15v1H1V1H2V12.29L7.49,6.8l2,2L13.28,5H11V4Z"/></svg>