refactor: use react namespace imports

[devrnt]

Disable allowSyntheticDefaultImports in tsconfig so we have to use namespace import

• Reduce bundlesize because of React namespace imports: https://twitter.com/sebmarkbage/status/1250284377138802689

[github-actions]

Size Change: -77 B (0%)

Total Size: 9.27 kB

Filename	Size	Change
dist/react-use-intercom.cjs.development.js	3.47 kB	-58 B (1%)
dist/react-use-intercom.cjs.production.min.js	2.22 kB	-22 B (0%)
dist/react-use-intercom.esm.js	3.43 kB	+3 B (0%)

ℹ️ View Unchanged

Filename	Size	Change
dist/index.js	152 B	0 B

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