Re-introduce file splitting optimization

Code motion/splitting does not seem to work as expected and in some cases this causes non optimal chunks to be created.

Example:

entry-one.js
```js
export {foo2} from './file3.js'
```

entry-two.js
```js
export {foo} from './file3.js'
```

file3.js
```js
export const foo = 'foo';
export const foo2 = 'foo2';
```

The generated common chunk contains the following:
chunk-QXQWH7T5.js
```js
// file3.js
var foo = "foo";
var foo2 = "foo2";

export {
foo,
foo2
};
```

However, since `foo` and `foo2` are never referenced in the same entry-point, the expected behaviour would be that esbuild generates 2 chunks.

chunk-YYY.js
```js
// file3.js
var foo = "foo";

export {
foo
};
```
chunk-XXX.js

```js
// file3.js
var foo = "foo2";

export {
foo2
};
```

Repro https://esbuild.github.io/try/#YgAwLjE5LjgAewogIGJ1bmRsZTogdHJ1ZSwKICBzcGxpdHRpbmc6IHRydWUsCiAgZm9ybWF0OiAnZXNtJywKICBvdXRkaXI6ICcvJywKfQBlAGVudHJ5LW9uZS5qcwBleHBvcnQge2ZvbzIsIGZvbzN9IGZyb20gJy4vZmlsZTMuanMnAGUAZW50cnktdHdvLmpzAGV4cG9ydCB7Zm9vfSBmcm9tICcuL2ZpbGUzLmpzJwAAZmlsZTMuanMAZXhwb3J0IGNvbnN0IGZvbyA9ICdmb28nOwpleHBvcnQgY29uc3QgZm9vMiA9ICdmb28yJzsKZXhwb3J0IGZ1bmN0aW9uIGZvbzMgKCkge30

Version 0.19.8

Related to https://github.com/angular/angular-cli/issues/26622

Start by reproducing the example with the linked esbuild Try URL and the entry-one.js, entry-two.js, and file3.js inputs. Trace the code-splitting behavior for these re-exported symbols and verify that the completed change produces separate chunks containing only foo or foo2 rather than one shared chunk.

Written by the indexing model from the issue text.