It is the job of codegen backends to mark Decls that are referenced as
alive so that the frontend does not sweep them with the garbage. This
commit unifies the code between the backends with an added method on
Decl.
The implementation is more complete than before, switching on the Decl
val tag and recursing into sub-values.
As a result, two more array tests are passing.
Effectively a small continuation of #10152
This allows the for.zig behavior tests to pass. Unfortunately to fully test everything I had to move a lot of behavior tests from array.zig; most of them now pass (sorry @rainbowbismuth!)
I'm also conflicted on how I store constants into arrays because it's kind of stupid; array's can't be re-initialized using the same syntax, so instead of initializing each element, a new array is made which is copied into the destination. This also required that renderValue can't emit string literals for byte arrays given that they need to always have an extra byte for the NULL terminator, meaning that strings are no longer grep-able in the output.
