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.

build-android-arm64-v8a.sh

@@ -118,18 +118,6 @@ rm -rf install/lib/pkgconfig
 #   cd /data/local/tmp
 #   ./sherpa-onnx
 #
-# which shows the following error log:
-#
-#  CANNOT LINK EXECUTABLE "./sherpa-onnx": library "libsherpa-onnx-core.so" not found: needed by main executable
-#
-# Please run:
-#
-#  export LD_LIBRARY_PATH=$PWD:$LD_LIBRARY_PATH
-#
-# and then you can run:
-#
-#  ./sherpa-onnx
-#
 # It should show the help message of sherpa-onnx.
 #
 # Please use the above approach to copy model files to your phone.