When converting a for-loop to a loop, we were not cloning the for-loop's
body, but rather the statements within it. This worked fine, except if
we also hoisted a variable to a let within that body, which requires the
body to be cloned for the 'insert before' to work. This change clones
the for-loop body, which fixes the problem, but introduces a block in
the destination AST, which is ugly, but not incorrect.
Bug: tint:1300
Change-Id: I478244d87f8cf58837102004242ba1c835e21710
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/78821
Kokoro: Kokoro <noreply+kokoro@google.com>
Reviewed-by: Ben Clayton <bclayton@google.com>
Commit-Queue: Antonio Maiorano <amaiorano@google.com>
e1699caf81