fix: remove default theme type cast

[TimKolberger]

Closes #3314

📝 Description

This PR removes the typecast of the default chakra theme to ChakraTheme.

Type Theme was replaced by DefaultChakraTheme in the last release. This PR brings it back again and deprecates DefaultChakraTheme.

ChakaTheme is the definition how a theme looks like. Theme and former DefaultChakraTheme are the exact types of the default chakra theme.

💣 Is this a breaking change (Yes/No):

No, it brings back a removed type.

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[changeset-bot]

🦋 Changeset detected

Latest commit: 5a8d8c0

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 12 packages

Name	Type
@chakra-ui/theme	Patch
@chakra-ui/react	Patch
@chakra-ui/toast	Patch
@chakra-ui/test-utils	Patch
chakra-cra	Patch
gatsby-starter-default	Patch
chakra-nextjs	Patch
chakra-nextjs-ts	Patch
@chakra-ui/props-docs	Patch
@chakra-ui/docs	Patch

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