extensions: add unwrapfunction to undo wrapfunction Before this patch, we don't have a safe way to undo a wrapfunction because other extensions may wrap the same function and calling setattr will undo them accidentally. This patch adds an "unwrapfunction" to address the issue. It removes the wrapper from the wrapper chain, and re-wraps everything, which is not the most efficient but short and easy to understand. We can revisit the code if we have perf issues with long chains. The "undo" feature is useful in cases like wrapping a function just in a scope. Like, having a "select" command to interactively (using arrow keys) select content from some output (ex. smartlog). It could wrap "ui.label" to extract interesting texts just in the "select" command.