no-unused-prop-types: Crashes on indexable TypeScript prop declarations

[taion]

This is an issue with #2661 that makes it crash in certain cases. cc @eltonio450

Consider something like https://astexplorer.net/#/gist/dea688bfbbfb2b2a2ffc3b4e293e0a01/63d1542090fe4a6545194562b88ffa34d7b22c83.

The interface body here consists of a TSPropertySignature and a TSIndexSignature. The foundDeclaredPropertiesList is thus not actually a list of declared properties: https://github.com/yannickcr/eslint-plugin-react/pull/2661/files#diff-3ed4052fa9471077711e82f482c3f819R304

When iterating through them, attempting to access tsPropertySignature.key.name on the index signature in https://github.com/yannickcr/eslint-plugin-react/pull/2661/files#diff-3ed4052fa9471077711e82f482c3f819R317 fails, because the index signature has no key property.

[ljharb]

Thanks, the repro helped a lot. Will release a patch tomorrow.

[eltonio450]

whoah, it's been fast 😃 !

Thank you, and sorry for missing it :(

[ljharb]

v7.20.3 is released.