Build sherpa-onnx as a single shared library (#1078)

When `-D BUILD_SHARED_LIBS=ON` is passed to `cmake`, it builds a single shared library.

Specifically, 

- For C APIs, it builds `libsherpa-onnx-c-api.so`
- For Python APIs, it builds `_sherpa_onnx.cpython-xx-xx.so`
- For Kotlin and Java APIs, it builds `libsherpa-onnx-jni.so`

There is no `libsherpa-onnx-core.so` any longer.

Note it affects only shared libraries.

.github/workflows/test-dart.yaml

@@ -70,7 +70,7 @@ jobs:
           cd build
 
           cmake \
-            -D BUILD_SHARED_LIBS=ON \
+            -DBUILD_SHARED_LIBS=ON \
             -DSHERPA_ONNX_ENABLE_PORTAUDIO=OFF \
             -DSHERPA_ONNX_ENABLE_WEBSOCKET=OFF \
             -DBUILD_ESPEAK_NG_EXE=OFF \