Optimize stack variables annotation and enable it by default

[xusheng6]

Stack variable annotation is a cool feature that combines stack and dynamic analysis. However, due to various bugs, it has to be disabled by default for now.

We should really fix it so that:

1. The data variables are only update when necessary. E.g., if the user single stepped, do not update it

2. Do not overwrite user changes. When the annotations are wrong, the user would override it, however, the user changes will be overwritten by new annotations in the next update

3. Explore ways to render it without creating the data variables