Disconnects Store state fields from Compiler (#1761)

*  Moves CodeMemory, VMInterrupts and SignatureRegistry from Compiler
*  CompiledModule holds CodeMemory and GdbJitImageRegistration
*  Store keeps track of its JIT code
*  Makes "jit_int.rs" stuff Send+Sync
*  Adds the threads example.

crates/c-api/include/wasmtime.h

@@ -244,6 +244,7 @@ WASM_API_EXTERN own wasmtime_error_t *wasmtime_global_set(
 // instance is returned), or an instance can be returned (meaning no error or
 // trap is returned).
 WASM_API_EXTERN own wasmtime_error_t *wasmtime_instance_new(
+    wasm_store_t *store,
     const wasm_module_t *module,
     const wasm_extern_t* const imports[],
     size_t num_imports,