Add top level `$eval(script=)` helper method to Chromote Session

[schloerke]

$eval() alters the default behavior to have

• awaitPromise = TRUE: Wait for returned Promise object to resolve.
• returnByValue = TRUE: Return serialized values, not the pointer to the execution.

Questions:

• [ ] Should arguments be added? If so, this would require wrapping script in paste0("(function() { ", script, " }).apply(null, ", args_serialized, ");") which would have different scoping and return x; behavior.
• [ ] Should code be wrapped in { to scope let/const variables?