Add Flutter emulator tasks

[Ruslan660]

Summary

• Add a task template for listing Flutter emulators
• Add a task template for launching the default iOS simulator via apple_ios_simulator

Android emulator launch tasks are not included because Android emulator IDs are user-specific.

Verification

• jq empty languages/dart/tasks.json
• cargo fmt -- --check
• cargo check
• cargo build --target wasm32-wasip1 --release
• git diff --check

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[cla-bot]

We require contributors to sign our Contributor License Agreement, and we don't have @Ruslan660 on file. You can sign our CLA at https://zed.dev/cla. Once you've signed, post a comment here that says '@cla-bot check'.

[cla-bot]

We require contributors to sign our Contributor License Agreement, and we don't have @Ruslan660 on file. You can sign our CLA at https://zed.dev/cla. Once you've signed, post a comment here that says '@cla-bot check'.