Introduce a Q::Compunit type

[masak]

Q::Compunit would basically be very similar to Q::Literal::Block.

Right now the compunit is added at the last moment as the program is run.

    my $compunit = Val::Block.new(
        :$statements,
        :outer-frame(self.current-frame));
    self.enter($compunit);

Also, the Q::Statements type gets to hold the static lexpads, simply because there's no higher level to put it because we're missing a root level above statements to hang it on.

The AST tests would all need to be modified, but in a very mechanical fashion.

• add back Q::CompUnit
• put the static lexpads on blocks, not statementlists

[masak]

Or, better yet, instead of putting a root compunit node in all of the AST specifications, we just modify the read() sub in 007::Test. That way, we wouldn't even need a compunit mapping in %qclass_lookup — not unless we wanted to check for erroneous things, anyway.

[masak]

Fun historical fact: Q::CompUnit did exist from the start of 007, but was removed in 39db04a. Now it exists again.