[jest-preset] Fix mock for Linking

[jzaefferer]

Summary:

All three patched methods are supposed to return Promise<any>. Having the mock return undefined for them breaks tests that expect the Promise.

Changelog:

[General] [Fixed] - Fix mock for Linking methods to return Promises

Test Plan

I'm using this patch on my own project, it works fine there. I don't think it's worth trying to write an automated test for this.

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[react-native-bot]

This PR is stale because it has been open for 180 days with no activity. It will be closed in 7 days unless you comment on it or remove the "Stale" label.

[jzaefferer]

GitHub claimed there were merge conflicts. There weren't, but I rebased it anyway.

Would be great to get this merged, so I don't have to maintain this patch in two places. Or fight off the bot adding the stale label.