The Slice Compiler Should be More Tolerant of Metadata Placement

[InsertCreativityHere]

I really want to be able to write this:

interface foo
{
    void myOp(["java:identifier:java_continue"] out int continue);
}

But that causes a syntax error, and this is the correct way to write it:

interface foo
{
    void myOp(out ["java:identifier:java_continue"] int continue);
}

I suspect there's a similar issue with other modifier keywords.
We should change the Slice compiler to either:

1. Always require the metadata to be "at the front" of a Slice 'statement'.
2. Allow arbitrary mixing of metadata/modifier keywords (ie. you can have <metadata> out or out <metadata>, or heck, even <metadata> out <metadata>.