Switching to the code tab when the workspace has blocks causes "Save Now"

[kchadha]

Expected Behavior

Switching to the code tab should not ever cause "Save Now" to appear in the menu bar.

Actual Behavior

It does when there are blocks on the workspace.

Upon preliminary investigation, it appears that all the blocks on the workspace are being deleted and re-created (even in the VM).

We should investigate how this scenario is different from just switching between sprites (with the exception of duplicated sprites which currently have a bug -- see scratchfoundation/scratch-vm#2028).