Replace call-stack based AST traversal code with heap-stack based traversal

[keyboardDrummer]

We current use threads with very large stack sizes to prevent getting a stack overflow when traversing deep ASTs. However, it would be better to change these traversals so they don't use the call-stack for going into nested code.

The test nesting.bpl triggers some traversals of deeply nested code, and without using large stacks this test fails to pass.

PR #709 is a WIP attempt at using a stack on the heap

[shazqadeer]

I am trying to understand the connection between the two pull requests #710 and #709 . Is #710 a temporary measure which would become unnecessary once #709 lands?

[keyboardDrummer]

If #709 lands, #710 would become obsolete yes. However, I'm not sure when I'll have time to finish #709.

[keyboardDrummer]

Same issue, albeit with different information: dafny-lang/dafny#5471