add Dart 3.0.1 package

[lohanidamodar]

Checklist:

• [x] The package builds locally with ./piston build-pkg dart 3.0.1
• [x] The package installs with ./piston ppman install dart=3.0.1
• [x] The package runs the test code with ./piston run dart -l 3.0.1 packages/dart/3.0.1/test.*
• [x] Package files are placed in the correct directory
• [x] No old package versions are removed
• [x] All source files are deleted in the build.sh script
• [x] metadata.json's language and version fields match the directory path
• [x] Any extensions the language may use are set as aliases
• [x] Any alternative names the language is referred to are set as aliases.