Rename `wasm2asm` to `wasm2js`, emit ESM by default (#1642)

* Rename the `wasm2asm` tool to `wasm2js`

This commit performs a relatively simple rename of the `wasm2asm` tool to
`wasm2js`. The functionality of the tool doesn't change just yet but it's
intended that we'll start generating an ES module instead of just an `asm.js`
function soon.

* wasm2js: Support `*.wasm` input files

Previously `wasm2js` only supported `*.wast` files but to make it a bit easier
to use in tooling pipelines this commit adds support for reading in a `*.wasm`
file directly. Determining which parser to use depends on the input filename,
where the binary parser is used with `*.wasm` files and the wast parser is used
for all other files.

* wasm2js: Emit ESM imports/exports by default

This commit alters the default behavior of `wasm2js` to emit an ESM by default,
either importing items from the environment or exporting. Items like
initialization of memory are also handled here.

1 files changed, 32 insertions, 0 deletions

diff --git a/scripts/test/node-esm-loader.mjs b/scripts/test/node-esm-loader.mjs
new file mode 100644
index 000000000..73ff47800
--- /dev/null
+++ b/scripts/test/node-esm-loader.mjs
@@ -0,0 +1,32 @@
+// originally lifted from https://nodejs.org/api/esm.html
+
+import path from 'path';
+import process from 'process';
+import Module from 'module';
+
+const builtins = Module.builtinModules;
+
+const baseURL = new URL('file://');
+baseURL.pathname = `${process.cwd()}/`;
+
+export function resolve(specifier, parentModuleURL = baseURL, defaultResolve) {
+  if (builtins.includes(specifier)) {
+    return {
+      url: specifier,
+      format: 'builtin'
+    };
+  }
+  // Resolve the 'spectest' module to our special module which has some builtins
+  if (specifier == 'spectest') {
+    const resolved = new URL('./scripts/test/spectest.js', parentModuleURL);
+    return {
+      url: resolved.href,
+      format: 'esm'
+    };
+  }
+  const resolved = new URL(specifier, parentModuleURL);
+  return {
+    url: resolved.href,
+    format: 'esm'
+  };
+}