wamr-python: Enable debugging WASM and grant dir access (#2449)

- Enable debugging a WASM loaded and executed from Python.
- Expose API to enable access to list of host directories. Similar to --dir in iwasm.
- Add another python language binding sample: native-symbol.

language-bindings/python/wamr-api/samples/native-symbol/README.md

@@ -0,0 +1,44 @@
+# Native Symbol
+
+This sample demonstrates how to declare a Python function as `NativeSymbol`.
+
+Steps of the example:
+1. Load WASM from Python
+2. Call `c_func` from WASM.
+3. `c_func` calls `python_func` from Python.
+4. `python_func` calls `add` from WASM.
+5. Result shown by Python.
+
+## Build
+
+Follow instructions [build wamr Python package](../../README.md). 
+
+Compile WASM app example,
+
+```sh
+./compile.sh
+```
+
+## Run sample
+
+```sh
+python main.py
+```
+
+Output:
+
+```
+python: calling c_func(10)
+c: in c_func with input: 10
+c: calling python_func(11)
+python: in python_func with input: 11
+python: calling add(11, 1000)
+python: result from add: 1011
+c: result from python_func: 1012
+c: returning 1013
+python: result from c_func: 1013
+deleting ExecEnv
+deleting Instance
+deleting Module
+deleting Engine
+```