Missing size immediate in `array.new_fixed`

[kripken]

Discussed in #5768

^{Originally posted by patrick96 June 13, 2023}
It looks like the parser used in wasm-as does not support providing the size of the array in the array.new_fixed instruction as an immediate value. Is that intentional?

From what I can tell from the GC MVP document, an immediate value is required as part of the instruction. Their test suite seems to confirm this:

https://github.com/WebAssembly/gc/blob/099b55020af2ac29fb6f2886581de057d7372b02/test/core/gc/array.wast#L112-L114

I just wanted to first check whether there is a reason for this. I'm happy to open up a proper bug report if anyone thinks this should be looked into.