Issue description: Contains two fixes to DevTools related to making dart2wasm the default compiler. 1) Fixes adding compiler=js query param as an escape hatch to revert to dart2js and 2) correctly maps legacy urls format with compiler query param in them.
Why cherry-pick: The 2.54 release of DevTools makes the dart2wasm build the default. These two fixes ensure a smooth rollout of the dart2wasm build.