Compile Binaryen to WebAssembly (#2503)

This PR enables compiling Binaryen to WebAssembly when building binaryen.js. Since WebAssembly is best compiled and instantiated asynchronously in browsers, it also adds a new mechanism to tell if respectively when the module is ready by means of one of the following:

// Using a promise
const binaryen = require("binaryen");
binaryen.ready.then(() => {
  ... use normally ...
});

// Using await
const binaryen = require("binaryen");
(async () => {
  await binaryen.ready;
  ... use normally ...
})();

// Where top-level await is available
const binaryen = await require("binaryen").ready;
... use normally ...

One can also tell if Binaryen is already ready (for example when assuming it in follow-up code) by:

if (/* we already know that */ binaryen.isReady) {
  ... use normally ...
} else {
  throw Error("Binaryen is supposed to be ready here but isn't");
}

The JS test cases have been updated accordingly by wrapping everything in a test function and invoking it once ready. Documentation will have to be updated as well to cover this of course. New file size is about 2.5mb, even though the Wasm becomes inlined into the JS file which makes distribution across different environments a lot easier.

Also makes building binaryen (to either js or wasm) emit binaryen.js, and not binaryen_js.js etc.

Supersedes and thus fixes #1381
With .ready it also fixes #2452

1 files changed, 1 insertions, 0 deletions

diff --git a/.gitattributes b/.gitattributes
index dfdb8b771..ba181f19d 100644
--- a/.gitattributes
+++ b/.gitattributes
@@ -1 +1,2 @@
 *.sh text eol=lf
+test/binaryen.js/*.txt text eol=lf