Support macOS 10.15+

[ywu2014]

opencv_dart version is opencv_dart: ^1.2.4, but when i start app using command
flutter run -d macos
it shows Failed to load dynamic library 'libopencv_dart.dylib': dlopen failed: library "libopencv_dart.dylib" not found
the readme document said it will download libs auto automatically, but it didn't fot me.

so i manually run commands below

flutter pub add opencv_dart
dart run opencv_dart:setup macos --arch x64

and it did download libs，but still show "libopencv_dart.dylib" not found

then i set the lib environment below

export OPENCV_DART_DISABLE_AUTO_BUILD=1
export OPENCV_DART_LIB_PATH=/Users/ywu/.pub-cache/hosted/pub.flutter-io.cn/opencv_dart-1.2.4/macos/GNUSparseFile.0/libopencv_dart.dylib

and this time，it shows no suitable image found

my os version is macOS Catalina 10.15.7

[rainyl]

@ywu2014 The minimum supported macos version is 11.0, I will try to support 10.15, you can try to build the project by yourself for now.

[ywu2014]

thx，then about what time will you support 10.15，is there a general plan？

[rainyl]

I am migrating the entire build system to cmake, including opencv.full, the most important dependency is ffmpeg, since github doesnt provide macos 10.15 runner, ffmpeg needs to be properly configured, also I am planning to support ffmpeg on android and ios, so it may take a long time to finish.

[ywu2014]

@rainyl OK，thx！

[rainyl]

Never mind.

I am going to reopen this issue to remind myself, hope you wont mind it.

[ywu2014]

No problem!

[rainyl]

opencv_dart and opencv_core version v1.3.0 have been published, with macos 10.15 and above supported.