parsing command substitution inside parameter expansion in interactive shell

[Grisha Levit]

If a command substitution inside a parameter expansion has a command
followed by a newline, bash prints an error message (though the
command is parsed and saved in the history list correctly):

bash --norc -in <<<$'${_+$(:\n)}\n!!'
$ ${_+$(:
bash: command substitution: line 3: unexpected EOF while looking for
matching `)'
> )}
$ !!
${_+$(:; )}

If the command substitution starts with a newline, no error is printed
but the command is _not_ saved correctly to the history list (a
semicolon is inserted at the start):

bash --norc -in <<<$'${_+$(\n:)}\n!!'
$ ${_+$(
> :)}
$ !!
${_+$(; :)}