add wasmModule option to initialize JS API

[evanw]

The initialize JS API must be called when using esbuild in the browser to provide the WebAssembly module for esbuild to use. Previously the only way to do that was using the wasmURL API option like this:

await esbuild.initialize({
  wasmURL: '/node_modules/esbuild-wasm/esbuild.wasm',
})
console.log(await esbuild.transform('1+2'))

With this PR, you can now also initialize esbuild using a WebAssembly.Module instance using the wasmModule API option instead. The example above is equivalent to the following code:

await esbuild.initialize({
  wasmModule: await WebAssembly.compileStreaming(fetch('/node_modules/esbuild-wasm/esbuild.wasm'))
})
console.log(await esbuild.transform('1+2'))

This could be useful for environments where you want more control over how the WebAssembly download happens or where downloading the WebAssembly module is not possible.

Fixes #1093