Add knobs to limit memories/tables in a Store

Fuzzing has turned up that module linking can create large amounts of
tables and memories in addition to instances. For example if N instances
are allowed and M tables are allowed per-instance, then currently
wasmtime allows MxN tables (which is quite a lot). This is causing some
wasm-smith-generated modules to exceed resource limits while fuzzing!

This commits adds corresponding `max_tables` and `max_memories`
functions to sit alongside the `max_instances` configuration.
Additionally fuzzing now by default configures all of these to a
somewhat low value to avoid too much resource usage while fuzzing.

crates/fuzzing/src/generators.rs

@@ -75,7 +75,7 @@ pub struct Config {
 impl Config {
     /// Converts this to a `wasmtime::Config` object
     pub fn to_wasmtime(&self) -> wasmtime::Config {
-        let mut cfg = wasmtime::Config::new();
+        let mut cfg = crate::fuzz_default_config(wasmtime::Strategy::Auto).unwrap();
         cfg.debug_info(self.debug_info)
             .static_memory_maximum_size(self.static_memory_maximum_size.unwrap_or(0).into())
             .static_memory_guard_size(self.static_memory_guard_size.unwrap_or(0).into())

crates/fuzzing/src/lib.rs

@@ -39,6 +39,9 @@ pub fn fuzz_default_config(strategy: wasmtime::Strategy) -> anyhow::Result<wasmt
         .wasm_bulk_memory(true)
         .wasm_reference_types(true)
         .wasm_module_linking(true)
+        .max_instances(100)
+        .max_tables(100)
+        .max_memories(100)
         .strategy(strategy)?;
     Ok(config)
 }

crates/fuzzing/src/oracles.rs

@@ -101,6 +101,9 @@ pub fn instantiate_with_config(
         Ok(_) => {}
         // Allow traps which can happen normally with `unreachable`
         Err(e) if e.downcast_ref::<Trap>().is_some() => {}
+        // Allow resource exhaustion since this is something that our wasm-smith
+        // generator doesn't guarantee is forbidden.
+        Err(e) if e.to_string().contains("resource limit exceeded") => {}
         Err(e) => panic!("failed to instantiate {}", e),
     }
 }