Remove usage of PossiblyWeakSet from createEventHandle

[trueadm]

As mentioned by @gaearon in #19174 (comment):

Does this mean we leak memory on IE11? It looks like we always add targets to this Set, but it's never cleared (since it's assumed to be a WeakSet in modern browsers).

This is correct. To avoid this memory leak, we can avoid usage of WeakSet entirely and instead use a property on the target itself, which should allow for the target to be garbage collected properly.

[sizebot]

Details of bundled changes.

Comparing: d2e914a...90a42a7

react-dom

File	Filesize Diff	Gzip Diff	Prev Size	Current Size	Prev Gzip	Current Gzip	ENV
ReactDOMForked-prod.js	🔺+0.1%	🔺+0.1%	379.61 KB	379.99 KB	70.12 KB	70.18 KB	FB_WWW_PROD
react-dom-server.node.development.js	0.0%	0.0%	138.59 KB	138.59 KB	36.59 KB	36.6 KB	NODE_DEV
react-dom.production.min.js	0.0%	0.0%	124.35 KB	124.35 KB	39.9 KB	39.91 KB	NODE_PROD
ReactDOMForked-profiling.js	+0.1%	+0.1%	392.99 KB	393.36 KB	72.59 KB	72.66 KB	FB_WWW_PROFILING
ReactDOMTesting-dev.js	0.0%	0.0%	924.03 KB	924.47 KB	207.64 KB	207.7 KB	FB_WWW_DEV
react-dom-test-utils.development.js	0.0%	-0.0%	61.1 KB	61.1 KB	17.75 KB	17.75 KB	NODE_DEV
ReactDOMTesting-prod.js	🔺+0.1%	🔺+0.1%	380.76 KB	381.13 KB	71.53 KB	71.59 KB	FB_WWW_PROD
react-dom-unstable-fizz.node.development.js	0.0%	-0.1%	5.52 KB	5.52 KB	1.84 KB	1.84 KB	NODE_DEV
react-dom-unstable-fizz.browser.development.js	0.0%	+0.1%	5.25 KB	5.25 KB	1.78 KB	1.78 KB	UMD_DEV
react-dom-unstable-fizz.node.production.min.js	0.0%	🔺+0.1%	1.17 KB	1.17 KB	667 B	668 B	NODE_PROD
react-dom-unstable-fizz.browser.production.min.js	0.0%	🔺+0.1%	1.22 KB	1.22 KB	712 B	713 B	UMD_PROD
react-dom-unstable-fizz.browser.development.js	0.0%	+0.1%	4.78 KB	4.78 KB	1.68 KB	1.68 KB	NODE_DEV
react-dom.development.js	0.0%	0.0%	963.36 KB	963.36 KB	210.68 KB	210.68 KB	UMD_DEV
react-dom.production.min.js	0.0%	0.0%	124.25 KB	124.25 KB	40.67 KB	40.67 KB	UMD_PROD
react-dom.profiling.min.js	0.0%	0.0%	129.51 KB	129.51 KB	42.3 KB	42.3 KB	UMD_PROFILING
ReactDOMForked-dev.js	0.0%	0.0%	963.75 KB	964.2 KB	214.11 KB	214.18 KB	FB_WWW_DEV
react-dom.profiling.min.js	0.0%	0.0%	129.8 KB	129.8 KB	41.53 KB	41.53 KB	NODE_PROFILING
ReactDOM-dev.js	0.0%	0.0%	962.98 KB	963.42 KB	214.72 KB	214.78 KB	FB_WWW_DEV
ReactDOM-prod.js	🔺+0.1%	🔺+0.1%	379.15 KB	379.53 KB	69.9 KB	69.96 KB	FB_WWW_PROD
react-dom-server.browser.development.js	0.0%	0.0%	137.32 KB	137.32 KB	36.34 KB	36.34 KB	NODE_DEV
ReactDOM-profiling.js	+0.1%	+0.1%	392.23 KB	392.61 KB	72.28 KB	72.35 KB	FB_WWW_PROFILING
ReactDOMServer-dev.js	0.0%	0.0%	141.5 KB	141.5 KB	36.29 KB	36.29 KB	FB_WWW_DEV
react-dom-test-utils.development.js	0.0%	0.0%	66.1 KB	66.1 KB	18.24 KB	18.24 KB	UMD_DEV

Size changes (experimental)

Generated by 🚫 dangerJS against 90a42a7

[sizebot]

Details of bundled changes.

Comparing: d2e914a...90a42a7

react-dom

File	Filesize Diff	Gzip Diff	Prev Size	Current Size	Prev Gzip	Current Gzip	ENV
react-dom.development.js	0.0%	-0.0%	881.27 KB	881.27 KB	201.58 KB	201.57 KB	NODE_DEV
ReactDOMForked-prod.js	🔺+0.1%	🔺+0.1%	390.78 KB	391.15 KB	71.84 KB	71.91 KB	FB_WWW_PROD
react-dom-server.node.development.js	0.0%	-0.0%	137.08 KB	137.08 KB	36.38 KB	36.38 KB	NODE_DEV
ReactDOMForked-profiling.js	+0.1%	+0.1%	404.2 KB	404.58 KB	74.31 KB	74.38 KB	FB_WWW_PROFILING
react-dom-server.node.production.min.js	0.0%	-0.0%	20.2 KB	20.2 KB	7.58 KB	7.58 KB	NODE_PROD
ReactDOMTesting-dev.js	0.0%	0.0%	952.11 KB	952.56 KB	213.14 KB	213.21 KB	FB_WWW_DEV
ReactDOMTesting-prod.js	🔺+0.1%	🔺+0.1%	393.4 KB	393.78 KB	73.6 KB	73.67 KB	FB_WWW_PROD
react-dom-test-utils.production.min.js	0.0%	-0.0%	12.67 KB	12.67 KB	4.96 KB	4.96 KB	NODE_PROD
react-dom.development.js	0.0%	-0.0%	925.84 KB	925.84 KB	204.04 KB	204.04 KB	UMD_DEV
react-dom.profiling.min.js	0.0%	0.0%	123.59 KB	123.59 KB	40.48 KB	40.48 KB	UMD_PROFILING
ReactDOMForked-dev.js	0.0%	0.0%	989.27 KB	989.72 KB	218.89 KB	218.96 KB	FB_WWW_DEV
react-dom-server.browser.production.min.js	0.0%	-0.0%	19.88 KB	19.88 KB	7.46 KB	7.46 KB	UMD_PROD
ReactDOM-dev.js	0.0%	0.0%	988.5 KB	988.94 KB	219.44 KB	219.51 KB	FB_WWW_DEV
ReactDOM-prod.js	🔺+0.1%	🔺+0.1%	390.31 KB	390.69 KB	71.58 KB	71.65 KB	FB_WWW_PROD
react-dom-server.browser.development.js	0.0%	-0.0%	135.81 KB	135.81 KB	36.13 KB	36.13 KB	NODE_DEV
ReactDOM-profiling.js	+0.1%	+0.1%	403.44 KB	403.82 KB	74 KB	74.06 KB	FB_WWW_PROFILING
react-dom-server.browser.production.min.js	0.0%	-0.0%	19.78 KB	19.78 KB	7.42 KB	7.42 KB	NODE_PROD
ReactDOMServer-dev.js	0.0%	-0.0%	145.53 KB	145.53 KB	37.3 KB	37.3 KB	FB_WWW_DEV
ReactDOMServer-prod.js	0.0%	-0.0%	47.3 KB	47.3 KB	11.04 KB	11.03 KB	FB_WWW_PROD

Size changes (stable)

Generated by 🚫 dangerJS against 90a42a7

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