Use external process to generate componentize-py wasm binary

Invoking the `componentize_py.componentize()` directly in process was
affecting the state of wasmtime somehow that resulted in
`test_instance.py` failing:

```
tests/test_instance.py ............Fatal Python error: Illegal instruction

Current thread 0x00000001e8d86100 (most recent call first):
  File "wasmtime-py/wasmtime/_bindings.py", line 2792 in wasmtime_instance_new
  File "wasmtime-py/wasmtime/_instance.py", line 34 in __init__
  File "wasmtime-py/tests/test_instance.py", line 179 in test_start_trap
Illegal instruction: 4
```

Don't know the root cause, but calling `componentize-py` in a separate
process fixes this issue.

tests/bindgen/__init__.py

@@ -67,9 +67,10 @@ def test_bare_funcs():
 from wasmtime.bindgen import generate
 import wasmtime
 import contextlib
-import componentize_py
 import importlib
 import tempfile
+import subprocess
+import shutil
 
 
 TEST_ROOT = Path(__file__).parent
@@ -111,20 +112,17 @@ def testsuite_name(self):
 
 def generate_bindings(testcase: BindgenTestCase):
     wit_path = testcase.wit_full_path
-    python_path = [str(testcase.app_dir)]
-    stub_wasi = True
+    componentize_py = shutil.which('componentize-py')
+    if componentize_py is None:
+        raise RuntimeError("Could not find componentize-py executable.")
     with tempfile.NamedTemporaryFile('w') as f:
         output_wasm = str(f.name + '.wasm')
         with chdir(testcase.app_dir):
-            componentize_py.componentize(wit_path,
-                                        testcase.world_name,
-                                        python_path,
-                                        [],
-                                        testcase.app_name,
-                                        output_wasm,
-                                         # isyswasfa=None
-                                        None,
-                                        stub_wasi)
+            subprocess.run([
+                componentize_py, '-d', str(wit_path), '-w', testcase.world_name,
+                'componentize', '--stub-wasi', testcase.app_name,
+                '-o', output_wasm
+            ], check=True)
             # Once we've done that now generate the python bindings.
             testsuite_name = testcase.testsuite_name
             with open(output_wasm, 'rb') as out: