Enable createEventHandle API for wWW test builds

[bvaughn]

Without this, Scott is unable to test the new test selector API because code that uses useEvent will cause null runtime errors (since createEventHandle returns null unless this flag is enabled).

[codesandbox-ci]

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Details of bundled changes.

Comparing: 1cbaf48...2d19a5b

react-dom

File	Filesize Diff	Gzip Diff	Prev Size	Current Size	Prev Gzip	Current Gzip	ENV
react-dom-server.node.development.js	0.0%	-0.0%	136.88 KB	136.88 KB	36.35 KB	36.35 KB	NODE_DEV
react-dom-server.browser.development.js	0.0%	-0.0%	142.96 KB	142.96 KB	36.55 KB	36.55 KB	UMD_DEV
react-dom-test-utils.production.min.js	0.0%	-0.0%	10.34 KB	10.34 KB	4.06 KB	4.06 KB	UMD_PROD
ReactDOMTesting-dev.js	+1.2%	+1.1%	962.65 KB	974.67 KB	215.75 KB	218.12 KB	FB_WWW_DEV
react-dom-test-utils.development.js	0.0%	-0.0%	51.13 KB	51.13 KB	14.89 KB	14.89 KB	NODE_DEV
ReactDOMTesting-prod.js	🔺+2.0%	🔺+1.8%	400.98 KB	408.89 KB	75.46 KB	76.85 KB	FB_WWW_PROD
react-dom-test-utils.production.min.js	0.0%	-0.0%	10.19 KB	10.19 KB	3.98 KB	3.98 KB	NODE_PROD
react-dom.development.js	0.0%	-0.0%	919.85 KB	919.85 KB	202.94 KB	202.93 KB	UMD_DEV
react-dom-server.browser.production.min.js	0.0%	-0.0%	19.88 KB	19.88 KB	7.45 KB	7.44 KB	UMD_PROD
react-dom-server.browser.development.js	0.0%	-0.0%	135.61 KB	135.61 KB	36.1 KB	36.1 KB	NODE_DEV
ReactDOMServer-prod.js	0.0%	-0.0%	47.44 KB	47.44 KB	11.11 KB	11.11 KB	FB_WWW_PROD

ReactDOM: size: 0.0%, gzip: -0.0%

Size changes (stable)

Generated by 🚫 dangerJS against 2d19a5b

[sizebot]

Details of bundled changes.

Comparing: 1cbaf48...2d19a5b

react-dom

File	Filesize Diff	Gzip Diff	Prev Size	Current Size	Prev Gzip	Current Gzip	ENV
react-dom.development.js	0.0%	-0.0%	905.93 KB	905.93 KB	206.09 KB	206.09 KB	NODE_DEV
react-dom-server.node.development.js	0.0%	-0.0%	138.39 KB	138.39 KB	36.56 KB	36.56 KB	NODE_DEV
react-dom-test-utils.production.min.js	0.0%	-0.0%	10.35 KB	10.35 KB	4.07 KB	4.07 KB	UMD_PROD
ReactDOMTesting-dev.js	+1.3%	+1.2%	934.63 KB	946.64 KB	209.86 KB	212.27 KB	FB_WWW_DEV
react-dom-test-utils.development.js	0.0%	-0.0%	51.15 KB	51.15 KB	14.9 KB	14.9 KB	NODE_DEV
ReactDOMTesting-prod.js	🔺+2.1%	🔺+2.1%	387.47 KB	395.73 KB	73.4 KB	74.94 KB	FB_WWW_PROD
react-dom-test-utils.production.min.js	0.0%	-0.0%	10.2 KB	10.2 KB	3.99 KB	3.99 KB	NODE_PROD
react-dom-unstable-fizz.node.production.min.js	0.0%	🔺+0.2%	1.17 KB	1.17 KB	665 B	666 B	NODE_PROD
react-dom-unstable-fizz.browser.production.min.js	0.0%	-0.1%	1.2 KB	1.2 KB	706 B	705 B	UMD_PROD
react-dom-unstable-fizz.browser.development.js	0.0%	-0.1%	4.87 KB	4.87 KB	1.71 KB	1.7 KB	NODE_DEV
react-dom.production.min.js	0.0%	-0.0%	122.91 KB	122.91 KB	40.19 KB	40.18 KB	UMD_PROD
react-dom.profiling.min.js	0.0%	-0.0%	126.85 KB	126.85 KB	41.38 KB	41.37 KB	UMD_PROFILING
ReactDOMForked-dev.js	0.0%	-0.0%	966.78 KB	966.78 KB	216.21 KB	216.21 KB	FB_WWW_DEV
react-dom-server.browser.development.js	0.0%	-0.0%	137.12 KB	137.12 KB	36.31 KB	36.31 KB	NODE_DEV
ReactDOMServer-dev.js	0.0%	0.0%	142.62 KB	142.62 KB	36.25 KB	36.25 KB	FB_WWW_DEV
react-dom-test-utils.development.js	0.0%	-0.0%	55.53 KB	55.53 KB	15.37 KB	15.37 KB	UMD_DEV

ReactDOM: size: 0.0%, gzip: -0.0%

Size changes (experimental)

Generated by 🚫 dangerJS against 2d19a5b