Add debugger alias for exec(expr)

[morenoh149]

node v9.8.0
In the debugger you can quickly inspect the value of a variable at run-time using exec. Given

// test.js
var a = 1

$ node inspect test.js
< Debugger listening on ws://127.0.0.1:9229/4565e728-272a-497d-a3f8-73b03362df0f
< For help see https://nodejs.org/en/docs/inspector
< Debugger attached.
Break on start in test.js:1
> 1 (function (exports, require, module, __filename, __dirname) { var a = 1
  2
  3 });
debug> n
break in test.js:1
> 1 (function (exports, require, module, __filename, __dirname) { var a = 1
  2
  3 });
debug> n
break in test.js:3
  1 (function (exports, require, module, __filename, __dirname) { var a = 1
  2
> 3 });
debug> exec('a')
1
debug> .exit

To more quickly debug an application it would be nice to alias exec to e or p so one can do

debug> p('a')
1

Even better if the expression could be passed without parens and quotes

debug> p a
1

This is in the same spirit as when pressing Enter the debugger will repeat the previous command.
From #20963

[jkrems]

Moving back to node since the code was merged into node itself. I think p a would be a reasonable short-hand to add though it would require somebody to send a PR to implement it.