This implements proper context switching while unwinding the stack due
to an exception being handled in interpreted code. The context under
which the handler is scoped is being preserved in a dedicated register
while the try-block is running. Both, the stack unwinding machinery as
well as the graph builder, restore the context from that register.

R=rmcilroy@chromium.org,bmeurer@chromium.org
BUG=v8:4674
LOG=n

Review URL: https://codereview.chromium.org/1665833002

Cr-Commit-Position: refs/heads/master@{#33733}