`ReadOnly`/`ArgMemOnly` were mostly moved over, but a few were missed.
Update them all. Also default to `unknown` for no memory effects rather
than none (ie. we should be conservative).
For each decl that needs a `#_hasSymbol()` query function, emit the corresponding helper function body during IRGen. Use `IRSymbolVisitor` to collect linkable symbols associated with the decl and return true from the helper function if the address of every associated symbol is non-null.
Resolves rdar://101884587
