Preview component should not rely on prop change detection to send expressions to frame #1322
Description
Currently the <Preview> component looks for changes in the list of console expressions to determine what if any expressions to send to the frame for evaluation. Component behavior that depends on both previous and current state is considerably harder to reason about and should be avoided. Instead, console entries should have state indicating whether they have been sent to a frame for evaluation; this should be updated synchronously after the frame initially posts the expression. The <Preview> component should simply consume all entries that are not marked as evaluation started.