wasm: support js string constant esm import

Extends the Wasm ESM Integration for importing WebAssembly
modules in either the source phase or instance phase to support
importing static JS string constants from the special
import name `wasm:js/string-constants`.

Author: guybedford

doc/api/esm.md

@@ -809,6 +809,15 @@ imports and they cannot be inspected via `WebAssembly.Module.imports(mod)`
 or virtualized unless recompiling the module using the direct
 `WebAssembly.compile` API with string builtins disabled.
 
+String constants may also be imported from the `wasm:js/string-constants` builtin
+import URL, allowing static JS string globals to be defined:
+
+```text
+(module
+  (import "wasm:js/string-constants" "hello" (global $hello externref))
+)
+```
+
 Importing a module in the source phase before it has been instantiated will also
 use the compile-time builtins automatically:
 

lib/internal/modules/esm/translators.js

@@ -522,6 +522,7 @@ translators.set('wasm', function(url, translateContext) {
   try {
     compiled = new WebAssembly.Module(source, {
       builtins: ['js-string'],
+      importedStringConstants: "wasm:js/string-constants"
     });
   } catch (err) {
     err.message = errPath(url) + ': ' + err.message;

test/fixtures/es-modules/js-string-builtins.wasm

@@ -4,11 +4,15 @@
   (import "wasm:js-string" "length" (func $string_length (param externref) (result i32)))
   (import "wasm:js-string" "concat" (func $string_concat (param externref externref) (result (ref extern))))
   (import "wasm:js-string" "equals" (func $string_equals (param externref externref) (result i32)))
+
+  ;; Import a string constant via importedStringConstants
+  (import "wasm:js/string-constants" "hello" (global $hello externref))
 
   ;; Export functions that use the builtins
   (export "getLength" (func $get_length))
   (export "concatStrings" (func $concat_strings))
   (export "compareStrings" (func $compare_strings))
+  (export "getHello" (func $get_hello))
 
   (func $get_length (param $str externref) (result i32)
     local.get $str
@@ -26,4 +30,8 @@
     local.get $str2
     call $string_equals
   )
+
+  (func $get_hello (result externref)
+    global.get $hello
+  )
 )

test/fixtures/es-modules/js-string-builtins.wat

@@ -6,3 +6,4 @@ strictEqual(wasmExports.getLength('hello'), 5);
 strictEqual(wasmExports.concatStrings('hello', ' world'), 'hello world');
 strictEqual(wasmExports.compareStrings('test', 'test'), 1);
 strictEqual(wasmExports.compareStrings('test', 'different'), 0);
+strictEqual(wasmExports.getHello(), 'hello');