staged concolic miniwasm

[butterunderflow]

The starting point of this PR is src/main/scala/wasm/StagedMiniWasm.scala, which is a staged interpreter of MiniWasm that generates C++ code.
By extending src/main/scala/wasm/StagedMiniWasm.scala with symbolic semantics, we got src/main/scala/wasm/StagedConcolicMiniWasm.scala, which is a concolic staged interpreter that generates concolic C++ code.
Combine the generated code with the runtime defined in headers/wasm/ we can achieve compiled concolic execution for WebAssembly.
The generated C++ code looks like this:

std::monostate Snippet(std::monostate x0) {
  // the logic of the entry function
  ...
}
int main(int argc, char *argv[]) {
  start_concolic_execution_with(Snippet, 2);
  return 0;
}

where Snippet is the generated concolic function corresponding to the entry
function of the input WebAssembly module, and start_concolic_execution_with a
C++ runtime function defined that manages the concolic execution process.

To test this feature, you can run:

sbt 'testOnly gensym.wasm.TestStagedConcolicEval'

To use this feature to compile a particular WebAssembly module, you can run this sbt test command:

INPUT=<path-to-your-wat-file> sbt 'testOnly gensym.wasm.TestBenchmark -- -z compile-a-single-file'

[ahuoguo]

TODO: if cons.s is SymVal.Concrete, then do not fork on Exploration Tree
A test case will be a straight line for an exploration tree with a bunch of SymVal

Same for If, BrTable, and other control flow constructs