1382: Test Refactor r=syrusakbary a=syrusakbary
# Description
This PR is the continuation of #1380.
It refactors our testing infrastructure based on various points:
* There is no longer a "default compiler" on tests
* Tests are automatically generated for: emscripten and wasi
* It accelerates testing into multiple threads when possible (with the exception of the llvm backend)
* It automatically detects the backends available in the host
Summary of changes:
* [x] Removed all extra logic for test creation in emscripten test generator
* [x] Removed all extra logic for test creation in the wasi test generator
* [x] Divided wasmer wast test in different files (under `tests/custom/`)
* [x] Refactored trap asserts using the wast format
* [x] Improved the build script by adding emscripten and wasi test generators (separated from build)
* [x] Improved WASI errors to be Rust error types (by deriving from `thiserror::Error`)
* [x] Fixed toolchain error creation
* [x] Removed leaking of testing logic from generators into build
* [x] Refactored import tests to be compatible with multiple backends
* [x] Improved wasmer binary to work even when no backends are set (useful for testing without any backend available).
* [x] Removed assumption that Cranelift will be the default in the `wasmer` binary
* [x] Migrated middleware
# Review
- [x] Add a short description of the the change to the CHANGELOG.md file
Co-authored-by: Syrus <me@syrusakbary.com>
Co-authored-by: Syrus Akbary <me@syrusakbary.com>
