WebAssembly release planning

[ppenzin]

This is a discussion to determine what should go into the next release w.r.t WebAssembly. We have updated the SIMD opcodes somewhat recently, and I am inclined to remove anything else that is not yet in from the upcoming release.

Things among open issues that are worth noting, in my opinion:

• #6524 - request to throw an exception when Wasm runs out of stack space, rather than just crashing. It is planned for the next release, but since we haven't gotten to it my feeling is that we should postpone it.
• #6434 - getting us up to speed with Wasm SIMD. It is more or less a project, as it add new webassembly instructions, and requires some backend support. It is an important milestone in Wasm support, and CC has more than half of that functionality working already.
• #6396 - obvious optimization of Wasm shuffles. It is needed in order to stop shuffles from being embarrassingly slow.
• Other Wasm features (project) - longer term work.

[ppenzin]

I've moved #6524 and #6396 to vNext.