Add console eval helpers (/$[_0-4]/)

[jaril]

Both Chrome and [Firefox] DevTools(https://developer.mozilla.org/en-US/docs/Tools/Web_Console/Helpers) have user-facing console helpers/utilities. Making sure we support those in Replay seems reasonable, especially for frequently used ones.

We can start with:

• $0: Should evaluate to the currently-inspected element in the Elements Tab.
• $_: Should evaluate to the result of the last evaluated expression in the console.

[abstractalgo]

Per https://developer.chrome.com/docs/devtools/console/utilities/#recent-many, it can go from $0 to $4.