Export three.js Stats module for re-use downstream

[jwnimmer-tri]

This increases the dist/main.min.js size from 2217504 bytes to 2219470 bytes (an increase of 1966 bytes, or 0.09%).

See also RobotLocomotion/drake#23730.

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This change is 

[jwnimmer-tri]

Reviewable status: 0 of 3 files reviewed, all discussions resolved

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src/index.js line 20 at r1 (raw file):

import {LineMaterial} from 'three/examples/jsm/lines/LineMaterial.js';
import {LineGeometry} from 'three/examples/jsm/lines/LineGeometry.js';
import Stats from 'three/examples/jsm/libs/stats.module.js';

FYI https://stackoverflow.com/questions/36795819/when-should-i-use-curly-braces-for-es6-import

[jwnimmer-tri]

+assignee:@SeanCurtis-TRI for review, please.

[SeanCurtis-TRI]

@SeanCurtis-TRI reviewed 3 of 3 files at r1, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @jwnimmer-tri)