Allow instance allocators control over module compilation.

This commit introduces two new methods on `InstanceAllocator`:

* `validate_module` - this method is used to validate a module after
  translation but before compilation. It will be used for the upcoming pooling
  allocator to ensure a module being compiled adheres to the limits of the
  allocator.

* `adjust_tunables` - this method is used to adjust the `Tunables` given the
  JIT compiler.  The pooling allocator will use this to force all memories to
  be static during compilation.

crates/environ/src/tunables.rs

@@ -27,6 +27,9 @@ pub struct Tunables {
     /// Whether or not fuel is enabled for generated code, meaning that fuel
     /// will be consumed every time a wasm instruction is executed.
     pub consume_fuel: bool,
+
+    /// Whether or not to treat the static memory bound as the maximum for unbounded heaps.
+    pub static_memory_bound_is_maximum: bool,
 }
 
 impl Default for Tunables {
@@ -62,6 +65,7 @@ impl Default for Tunables {
             parse_wasm_debuginfo: true,
             interruptable: false,
             consume_fuel: false,
+            static_memory_bound_is_maximum: false,
         }
     }
 }