parse expr is typepath outside parenthesis

[nadako]

I checked the usages of expr_next and looks like we're good to lose parenthesis around expr is Type.

The error message is quite cryptic in these cases currently:

{x;} is Bad;
function f() {} is Bad;

because it parses is as a normal identifier and then becomes confused about Bad going right after it.

TODO:

• Parse ComplexType instead of just TypePath, error on non-typepaths later on typing?
• AST representation (EIs, EBinop with ECheckType?)
• Precedence (e.g. @meta a is B should be like @meta a + b?)
• Also parse a !is B to avoid awkward parens for negation?
• Anything else?