[Feature request] Specify sourceURL in build without stdin

Hi! I noticed some weird issues with source maps and error stacktraces when using `executeJavaScript` in the Electron APIs. This is because this is effectively the same action as pasting the passed code into DevTools.

Take the following code (adapted from my own build scripts):

```js
// build.js
import * as esbuild from "esbuild";

/** @type {import("esbuild").BuildOptions} */
const esbuildConfig = {
entryPoints: ["./input.js"],
outfile: "./output.js",
sourcemap: "inline"
};

await esbuild.build(esbuildConfig);
```

```js
// input.js
try {
throw new Error("Test error");
} catch (e) {
console.log(e);
}
```

This produces the input verbatim, plus a `//# sourceMappingURL`, which is expected. But, when running this code in my program with `executeJavaScript`, I get the following stacktrace:

```
Error: Test error
at :2:9
(my code that ran executeJavaScript follows, redacted for brevity)
```

Anonymous! Not great. The source map seems to not be loading.

Now, if I add the line `//# sourceURL=blah.js` to the end of my output script:

```
Error: Test error
at input.js:2:9
(my code that ran executeJavaScript follows, redacted for brevity)
```

There's some weird behavior going on here where specifying a sourceURL in DevTools causes it to load the source map, even if the provided URL is garbage. I don't entirely know what causes this, but **TL;DR I want to be able to specify sourceURL in build without using stdin**.

The following does not work:

```js
// build.js
import * as esbuild from "esbuild";

/** @type {import("esbuild").BuildOptions} */
const esbuildConfig = {
entryPoints: ["./input.js"],
outfile: "./output.js",
sourcemap: "inline",
sourcefile: "blah.js"
};

await esbuild.build(esbuildConfig);
```

...because it expectedly errors with `Invalid option in build() call: "sourcefile"`, because this isn't supported by esbuild.