This adds the `close()` method to `DynamicLibrary`, which uses
`dlclose()` on Unix and `FreeLibrary` on Windows to close a dynamic FFI
library.
TEST=tests/ffi/dylib_close_test.dart
Closes https://github.com/dart-lang/sdk/issues/40159
Cq-Include-Trybots: luci.dart.try:vm-ffi-android-debug-arm-try,vm-ffi-android-debug-arm64c-try,vm-ffi-qemu-linux-release-riscv64-try,vm-ffi-qemu-linux-release-arm-try,dart2wasm-linux-d8-try,dart2wasm-linux-chrome-try,vm-reload-rollback-linux-debug-x64-try,vm-reload-linux-debug-x64-try,vm-win-debug-x64c-try,vm-win-debug-x64-try,vm-aot-android-release-arm_x64-try,vm-mac-debug-arm64-try,vm-mac-debug-x64-try,vm-asan-linux-release-x64-try,vm-aot-msan-linux-release-x64-try,vm-aot-android-release-arm64c-try,vm-aot-android-release-arm_x64-try,vm-aot-linux-debug-x64-try,vm-aot-linux-debug-x64c-try,vm-aot-mac-release-x64-try,vm-aot-mac-release-arm64-try,vm-aot-win-debug-x64c-try,vm-aot-win-release-x64-try
CoreLibraryReviewExempt: `dart:ffi` VM only API.
Change-Id: I73af98677b481902fe548bdcee56964a0195faf0
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/307680
Reviewed-by: Daco Harkes <dacoharkes@google.com>
Commit-Queue: Daco Harkes <dacoharkes@google.com>
Simon Binder
62488db4da