Use traps when checking initial table/memory bounds (#12929)

Instead of using a custom error string this enables fuzzing to, for
example, see that a `Trap` was returned and consider the fuzz test case
a normal failure. These code paths are only executed when `bulk_memory`
is disabled which is pretty rare, and also explains why it's come up in
fuzzing only just now after #12883.

Author: alexcrichton

crates/wasmtime/src/runtime/vm/instance/allocator.rs

@@ -517,7 +517,7 @@ fn check_table_init_bounds(
                 // Initializer is in bounds
             }
             _ => {
-                bail!("table out of bounds: elements segment does not fit")
+                bail!(Trap::TableOutOfBounds);
             }
         }
     }
@@ -627,7 +627,7 @@ fn check_memory_init_bounds(
                 // Initializer is in bounds
             }
             _ => {
-                bail!("memory out of bounds: data segment does not fit")
+                bail!(Trap::MemoryOutOfBounds);
             }
         }
     }