Add a small harness that just loads all wasms from a workspace directory

[graydon]

This is just a small test harness to help people who want to run simple testcases they've generated outside soroban. Put your wasm file in soroban-env-host/src/test/hostile_inputs and run cargo test test_misc_hostile_wasms and it should just pick your wasm up and attempt to instantiate and run it.

Requirements:

• The wasm has to have the normal contract metadata section on the front! Absent that it will be rejected immediately.
• The wasm of course has to comply with the limited profile soroban uses (few-if-any post-MVP features, no floating point, etc.)
• The wasm has to expose a 0-arg function called "test" which is the only thing the test tries to execute.