meta: rename ./dialects/abstract to ./abstract-dialect

[WikiRik]

Pull Request Checklist

• Have you added new tests to prevent regressions?
• If a documentation update is necessary, have you opened a PR to the documentation repository?
• Did you update the typescript typings accordingly (if applicable)?
• Does the description below contain a link to an existing issue (Closes #[issue]) or a description of the issue you are solving?
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Description of Changes

This PR moves the abstract dialect files to a higher level folder named abstract-dialect.

Only change not directly related to renaming the folder and updating imports is in packages/core/test/support.ts. That change is made possible because all natively supported dialects have their own package now.