Fix #3441: parentheses wrapping expression throw invalid error

[zdenko]

Fixes #3441.

Cases where statement is used inside parentheses don't compile:

(a(); break) for a in obj
# error: cannot use a pure statement in an expression
# (a(); break) for a in obj
#       ^^^^^

(a(); break) while a
# error: cannot use a pure statement in an expression
# (a(); break) while a
#       ^^^^^

for a in obj then (a(); break)
# error: cannot use a pure statement in an expression
# for a in obj then (a(); break)
#                         ^^^^^

while a then (a(); break)
# error: cannot use a pure statement in an expression
# while a then (a(); break)
#                    ^^^^^

With this PR:

# (a(); break) for a in obj
# for a in obj then (a(); break)
for (i = 0, len = obj.length; i < len; i++) {
  a = obj[i];
  a();
  break;
}

# (a(); break) while a
# while a then (a(); break)
while (a) {
  a();
  break;
}

When Parens block includes a StatementLiteral (e.g. (b; break) for a in arr), it won't compile since Parens ((b; break)) is compiled as Value and pure statement (break) can't be used in an expression.

This PR checks Parenthetical rule in the grammar and returns Block instead of Parens if StatementLiteral is detected. The Block node is passed further to the Expression.

[vendethiel]

I'd rather we don't add such code to the grammar. We can have a node function for that.

[vendethiel]

Also we try not to use constructor.name for obfuscation reasons IIRC.

[vendethiel]

you can use unwrap

[zdenko]

Nice.