dart: add page (#6351)

pages/common/dart.md

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+# dart
+
+> The tool for managing Dart projects.
+> More information: <https://dart.dev/tools/dart-tool>.
+
+- Initialize a new Dart project in a directory of the same name:
+
+`dart create {{project_name}}`
+
+- Run a Dart file:
+
+`dart run {{path/to/file.dart}}`
+
+- Download dependencies for the current project:
+
+`dart pub get`
+
+- Run unit tests for the current project:
+
+`dart test`
+
+- Update an outdated project's dependencies to support null-safety:
+
+`dart pub upgrade --null-safety`
+
+- Compile a Dart file to a native binary:
+
+`dart compile exe {{path/to/file.dart}}`