Specify allocation function by name instead of index

proposals/webidl-bindings/Explainer.md

@@ -191,8 +191,8 @@ tuple** of WebAssembly values.  A sample list of incoming binding operators:
 | :---     | :---       | :---     | :---        |
 | **get** | idx	| |	Return the `idx`th Web IDL value of the source tuple. |
 | **as** | wasm‑type | *in‑expr* | Take the result of `in-expr`, which can be any Web IDL value, and produces a wasm value of `wasm-type`, allowing only trivial conversions (like [`long`] to `i32` or [`any`] to `anyref`). |
-| **alloc‑utf8‑str** | alloc‑func‑idx | *in‑expr* | Take the result of `in-expr`, which must be either [`DOMString`] or [`USVString`], compute the number of bytes necessary to store a UTF-8 encoding of this string, call the `alloc-func-idx`'th function of the receiving instance, passing the number of bytes and using the resulting offset to store the UTF-8 encoding, as specified by [`TextEncoder`], finally returning the offset and byte-length as two `i32`s (and trapping on OOM). |
-| **alloc‑copy** | alloc‑func‑idx | *in‑expr* | Take the result of `in-expr`, which must be a [`BufferSource`] or [`ByteString`], call the `alloc-func-idx`'th function of the receiving instance, passing the length and using the resulting offset to store a copy of the bytes into linear memory, returning the offset and byte-length as two `i32`s (and trapping on OOM). |
+| **alloc‑utf8‑str** | alloc‑func‑name | *in‑expr* | Take the result of `in-expr`, which must be either [`DOMString`] or [`USVString`], compute the number of bytes necessary to store a UTF-8 encoding of this string, call the function exported by name `alloc-func-name` from the receiving instance, passing the number of bytes and using the resulting offset to store the UTF-8 encoding, as specified by [`TextEncoder`], finally returning the offset and byte-length as two `i32`s (and trapping on OOM). |
+| **alloc‑copy** | alloc‑func‑name | *in‑expr* | Take the result of `in-expr`, which must be a [`BufferSource`] or [`ByteString`], call the function exported by name `alloc-func-name` from the receiving instance, passing the length and using the resulting offset to store a copy of the bytes into linear memory, returning the offset and byte-length as two `i32`s (and trapping on OOM). |
 | **enum‑to‑i32** | webidl‑type | *in‑expr* | Take the result of `in-expr`, which must be an [Enumeration] value, and reverse-map this string to the `i32` index of the matching string in the `webidl-type`, which must also be an Enumeration. |
 | **field** | field‑idx | *in‑expr*	| Take the result of `in-expr`, which must be a [Dictionary] value, and return the Web IDL value of the `field-idx`'th field. |
 | **bind‑import** | wasm‑type<br>binding | *in‑expr* | Take the result of `in-expr`, which must be a [Callback] value, and apply `binding` to produce a [`funcref`]  (or, later, a typed function reference). (See [`BindImport`](#instantiation-and-runtime) below.) |