fix: use displayName for functional components

[skirtles-code]

Closes #690.

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The Transition component is shown as Anonymous Component in various places, e.g. in the component inspection tree:

This will now be shown as Transition instead:

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This fix also applies to other functional components with a displayName property.

Using the displayName in this way is consistent with how Vue core uses it:

• https://github.com/vuejs/core/blob/09dec962ae9c2e2ad49e584cef5f416a0d4558ff/packages/runtime-core/src/component.ts#L1215

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commit: 136e2d4