Refactor flutter to support Android (#1072)

flutter/sherpa_onnx_windows/windows/.gitignore

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+flutter/
+
+# Visual Studio user-specific files.
+*.suo
+*.user
+*.userosscache
+*.sln.docstates
+
+# Visual Studio build-related files.
+x64/
+x86/
+
+# Visual Studio cache files
+# files ending in .cache can be ignored
+*.[Cc]ache
+# but keep track of directories ending in .cache
+!*.[Cc]ache/

flutter/sherpa_onnx_windows/windows/CMakeLists.txt

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+# The Flutter tooling requires that developers have a version of Visual Studio
+# installed that includes CMake 3.14 or later. 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 3.14)
+
+# Project-level configuration.
+set(PROJECT_NAME "sherpa_onnx_windows")
+project(${PROJECT_NAME} LANGUAGES CXX)
+
+# List of absolute paths to libraries that should be bundled with the plugin.
+# This list could contain prebuilt libraries, or libraries created by an
+# external build triggered from this build file.
+set(sherpa_onnx_windows_bundled_libraries
+  "${CMAKE_CURRENT_SOURCE_DIR}/sherpa-onnx-c-api.dll"
+  "${CMAKE_CURRENT_SOURCE_DIR}/sherpa-onnx-core.dll"
+  "${CMAKE_CURRENT_SOURCE_DIR}/kaldi-decoder-core.dll"
+  "${CMAKE_CURRENT_SOURCE_DIR}/sherpa-onnx-kaldifst-core.dll"
+  "${CMAKE_CURRENT_SOURCE_DIR}/sherpa-onnx-fstfar.dll"
+  "${CMAKE_CURRENT_SOURCE_DIR}/sherpa-onnx-fst.dll"
+  "${CMAKE_CURRENT_SOURCE_DIR}/kaldi-native-fbank-core.dll"
+  "${CMAKE_CURRENT_SOURCE_DIR}/piper_phonemize.dll"
+  "${CMAKE_CURRENT_SOURCE_DIR}/espeak-ng.dll"
+  "${CMAKE_CURRENT_SOURCE_DIR}/ucd.dll"
+  "${CMAKE_CURRENT_SOURCE_DIR}/onnxruntime.dll"
+  "${CMAKE_CURRENT_SOURCE_DIR}/ssentencepiece_core.dll"
+  PARENT_SCOPE
+)

flutter/sherpa_onnx_windows/windows/README.md

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