Improve error message when matching on struct instantiation in match expressions

[ironcev]

This code:

let _ = match S { x: 0 } {
    _ => 0,
};

will produce a confusing error message saying:

let _ = match S { x: 0 } {
                   ^ Expected `=>`.

Improve the error message and provide useful hint, to put the struct instantiation inside of brackets:

let _ = match (S { x: 0 }) {
    _ => 0,
};