Support Unwind & With (#408)

* support unwind

* add test for case expr in ScannerTest

* add test for UnwindExecutor

* fix clang copy elision warning

* fix clang memory leak

* fix unwind executor

* support unwind return

* support with return

* improve MatchSolver:doRewrite

* support multi-clause unwind

* add CartesianProductStrategy

* fix CartesianProduct addVar bug

* fix RewriteMatchLabelVisitor::rewriteExprList bug

* fix unwind executor

* fix UnwindExecutor test

* check alias existence for with/unwind

* add WithUnwind.feature test

* address comments