Cryptic errors on missing/wrong braces

[bannmann]

Silverchain fails to parse the following AG files, which is correct. However, the error messages are overly generic and vague. I included some examples of what I would consider a helpful message.

// fails with the following error:
// line 13:15 no viable alternative at input 'Foo{voidfirstsecond'
//
// fix:
// replace "first" with "first()"
//
// ideas for helpful messages:
// - line 13:14 expected '(', got ' '
// - line 13:15 expected '(', got 'second'
// - line 13:9 expected METHOD_SIGNATURE, got TYPE_NAME
//
Foo {
    void first second() third();
}

// fails with the following error:
// line 15:15 no viable alternative at input 'Foo{voidfirst(secondA('
//
// fix:
// replace "first" with "first()"
//
// ideas for helpful messages:
// - line 15:15 unexpected opening brace
// - line 15:8 expected TYPE_NAME, got METHOD_SIGNATURE
// - line 15:8 expected PARAMETER, got METHOD_SIGNATURE
//
Foo {
    void
    first
    (
        secondA()
        |
        secondB()
    )
    third();
}