Rewrap to completion if function returns completion record type

[hyp3rflow]

The result type modified by Interpreter.setTypeMap needs to be rewrapped if the function returns completion record.
There are already many parts of our code do the same thing.

esmeta/src/main/scala/esmeta/analyzer/AbsTransfer.scala

Line 244 in a47e674

as.map(v => if (cp.func.isReturnComp) v.wrapCompletion else v)

esmeta/src/main/scala/esmeta/interpreter/Interpreter.scala

Line 552 in a47e674

if (st.context.func.isReturnComp) value.wrapCompletion else value,

... and more.

And this PR adds/moves some comments related with Implicit Normal Completion.

[jhnaldo]

LGTM! 👍🏻