Implemented lazy stack symbolization.

Implemented lazy stack symbolization.

Previously, when an exception was thrown, the exception got 'stack'
property attached which contained the backtrace information about where
the exception happened. This could be a heavy operation and it was not
always needed.

To optimize it, the process is split into 2 phases. The first phase
collects all the necessary info about the current stack. The second
phase, where the stack symbolization happens, occurs only when this
property is referenced.