[Lens] Optimize expression rendering

[wylieconlon]

There are some issues that are introduced here: #48841

Specifically in Lens, we are seeing:

• Switching an index pattern triggers new data to be fetched, even though the visualization is unchanged
• Sometimes an error state is shown, most likely because sending two render requests in a row will cause the first to get cancelled and show an error state.

This doesn't prevent Lens from working, but the behavior is inefficient and potentially confusing.

[elasticmachine]

Pinging @elastic/kibana-app (Team:KibanaApp)

[flash1293]

By memoizing on the expression and caching requests, this problem is resolved