[ddc] run expression evaluation canary tests on canary bots

[annagrin]

The canary js files are currently compiled into a different directory from the stable ones, and expression evaluation tests do not account for that.

• Make sure expression evaluation suite can find dart_sdk.js based on the mode (canary/stable)
• Split the expression evaluation tests into canary and stable ones
• Make sure stable and canary bots only run appropriate tests