…iftwasm#673)

Now `Optional` conforms to `_BridgedSwiftStackType` whenever `Wrapped`
conforms to `_BridgedSwiftStackType`. This makes generic programming
easier and reduces boilerplate in intrinsics and codegen.

For specialized handling of certain types like associated value enums,
where the presence of a value is encoded as a sentinel case ID (-1),
we implement `bridgeJSStack{Push,Pop}AsOptional` methods, which is on
the witness table of `_BridgedSwiftStackType`.

Also now some of optional types no longer pushes placeholders values for
`nil` cases when pushing in JS and popping in Swift.

…2a69522fb9941ebaf3ac11

BridgeJS: Remove inline array lifting/lowering codegen