Pointers should not be `DATA`: they can never be stored in anything. (Function
arguments are not storage; they're like `let` bindings.)
Un-`SIZED` values may only live in the `Storage` storage class, so creating
pointers to them in other storage classes is meaningless.
The `ARGUMENT` flag should be set only on pointers in those storage classes that
are permitted to be passed to functions.
See comments in code for details.
Fixes#1513.
The WGSL front end knows that globals in the `Handle` storage class do not
produce references, but it attempts to manage this in two places which trip over
each other. As a consequence, referring to a `let` binding holding a pointer to
a global flips the variable's type from WGSL `ptr` to WGSL reference, with
bewildering consequences.
The original pointer access test used SPIR-V for its input because WGSL didn't
have a working pointer indirection operator at the time. Now that it does, we
can just write this test in WGSL directly.
Fixes#1432.
Treat expressions in `Function::named_expressions` like WGSL `let` declarations,
assuming that the Load Rule was applied to the rhs of the declaration, meaning
that their values are always `Indirection::Ordinary`.
Split `write_expr_plain_form` out from `write_expr_with_indirection`, to clean
up the parenthesis generation: no more `opened_paren` variable, just function
calls. This makes the early return for named expressions neater.
Fixes#1382.
