chore(fuzzing): Improve wasm execution fuzzers

[venkkatesh-sekar]

This PR sends some love to the Wasm execution fuzzers, as they were in maintenance mode for some time and haven't caught up with the recent changes in the execution environment.

Production code changes:

1. Adds a new test method set_api_type to rs/embedders/src/wasmtime_embedder/system_api.rs to hot reload the ApiType for SystemApiImpl. (This affects some constants within the state as well, but I don't think they are necessary for the fuzzer).

execute_with_wasm_executor_afl

1. In the previous versions, WasmExecutionInput was created for every Wasm method executed, but this was done poorly. The CompilationCache was created fresh for each input, and thus the Wasm was compiled every time a method was executed. The current change utilizes WasmExecutor.create_execution_state to compile and instantiate the Wasm, and we pass the compilation_cache used here to WasmExecutionInput. This improves the fuzzer speed by 10x.
2. Every time a method was executed, a new ExecutionState was created, including the SystemState. To extend the coverage of the fuzzer, the result of the previous method's execution is persisted for the next method. This includes ExecutionState and SystemState, but the changes carried over are done conservatively. Precisely, this includes globals, wasm_memory, stable_memory, and balance changes in SystemState.
3. Previously, the ApiType was always set to Init, which was not right. To extend the coverage, we set the correct ApiType for the method, as this influences the system API responses.
4. The SystemState also contains a dummy call_context, as some system API operations like msg_cycles_accept panic without it (rightfully).

ic_wasm.rs

1. There was some machinery to extract exported_globals, since the previous version of execute_with_wasm_executor_afl required it. Since this is now done via WasmExecutor.create_execution_state, we can remove generating exported_globals from ICWasmModule.
2. wasm_smith::Config sets every new Wasm proposal to enabled, which created a lot of invalid Wasm. This is fine from the compiler fuzzer point of view, but the execution fuzzers don't require it. Hence, the struct is exhaustively listed, and the addition of new fields will fail compilation.
3. The ability to generate 32-bit system API is brought back (lost in some refactoring).

import.rs

The ability to generate 32-bit system API is brought back (lost in some refactoring).

compile.rs

SerializedModuleBytes is not required to be deterministic, and we set it as empty to hold the equality check for other fields.

execute_with_wasmtime_afl

ApiType change as above.

differential...

ApiType change as above.

We had excluded having a Cargo.toml for fuzzers in the hope of a Bazel solution for Rust Analyzer. The day hasn't come after years, so I have added a Cargo.toml for the wasm_fuzzers library, as this improves fixing issues a lot quicker.