Feature request: test-local variables in .wast

In a CG call a few weeks back, I mentioned that having the ability to have test-local variables in .wast files would be useful.

In particular, many tests that use reference types, mostly in proposals right now (such as function-references and gc use tables internal to a module and an initializer. These tests would be shorter, easier to write, and easier to debug (a key productivity boost for engine implementers) if the test itself could bind variables.

Exact details of syntax and semantics TBD.

Sketch:

(module
  (func "create_ref1" (result anyref))
  ...
  (func "take_ref" (param anyref) (result i32))
)

(test-local $ref1 anyref (invoke "create_ref1"))

(assert_return (invoke "take_ref" (test-local.get $ref1)) (i32.const 11))

That would remove the need for tables, but the issue of needing to create objects/functions inside a module (because types and decls live in modules) remains.

Start by reviewing the existing .wast test syntax in the reference interpreter and test suite, then compare how reference types, tables, and module initializers are represented. Define the test-local variable syntax and semantics, including how values are created and retrieved; done means the design is specified and covered by representative tests.