Refactor flutter to support Android (#1072)

flutter/sherpa_onnx_linux/linux/CMakeLists.txt

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+# The Flutter tooling requires that developers have CMake 3.10 or later
+# installed. You should not increase this version, as doing so will cause
+# the plugin to fail to compile for some customers of the plugin.
+cmake_minimum_required(VERSION 3.10)
+
+# Project-level configuration.
+set(PROJECT_NAME "sherpa_onnx_linux")
+project(${PROJECT_NAME} LANGUAGES CXX)
+
+# List of absolute paths to libraries that should be bundled with the plugin.
+# This list could contain prebuilt libraries, or libraries created by an
+# external build triggered from this build file.
+set(sherpa_onnx_linux_bundled_libraries
+  "${CMAKE_CURRENT_SOURCE_DIR}/libsherpa-onnx-c-api.so"
+  "${CMAKE_CURRENT_SOURCE_DIR}/libsherpa-onnx-core.so"
+  "${CMAKE_CURRENT_SOURCE_DIR}/libkaldi-decoder-core.so"
+  "${CMAKE_CURRENT_SOURCE_DIR}/libsherpa-onnx-kaldifst-core.so"
+  "${CMAKE_CURRENT_SOURCE_DIR}/libsherpa-onnx-fstfar.so"
+  "${CMAKE_CURRENT_SOURCE_DIR}/libsherpa-onnx-fst.so"
+  "${CMAKE_CURRENT_SOURCE_DIR}/libkaldi-native-fbank-core.so"
+  "${CMAKE_CURRENT_SOURCE_DIR}/libpiper_phonemize.so"
+  "${CMAKE_CURRENT_SOURCE_DIR}/libespeak-ng.so"
+  "${CMAKE_CURRENT_SOURCE_DIR}/libucd.so"
+  "${CMAKE_CURRENT_SOURCE_DIR}/libonnxruntime.so"
+  "${CMAKE_CURRENT_SOURCE_DIR}/libssentencepiece_core.so"
+  PARENT_SCOPE
+)

flutter/sherpa_onnx_linux/linux/README.md

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+# Introduction
+
+`*.so` files are generated dynamically using GitHub actions during a new release.
+
+We don't check-in pre-built library files into git.