refactor: remove *.d.ts files

[DavideMininni-Fincons]

Preflight Checklist

• I have read the Contributing Guidelines for this project.
• I agree to follow the Code of Conduct that this project adheres to.
• I have searched the pull request tracker for a Pull Request (PR) that matches the one I want to submit, without success.

Issue

This PR Closes #

Pull request checklist

Please check if your PR fulfills the following requirements:

• Tests for the changes have been added (for bug fixes / features)
• Docs have been reviewed and added / updated if needed (for bug fixes / features)

See Review Guidelines for more information what is checked during review process.

Changes

Changes in this pull request:

• all the .d.ts files have been removed;
• interfaces have been moved in the corresponding .tsx file, or, in some cases, in the .helper.ts file (sbb-image and others);
• general types which are used by more than one file (eg. 'orientation' or 'horizontalForm') have been merged in a single type in the newly created types.d.ts;
• types relative to a single component but used elsewhere (eg. the size in the sbb-button and sbb-link) are been changed to an exported type in the corresponding file;
• type used in a single file have been inlined in the .tsx
• there's a pending FIXME, but it requires to change an API (see sbb-timetable-travel-hints)

Browsers

I tested the build on the following browsers:

• Firefox Desktop
• Chrome Desktop
• Edge Desktop
• Safari Desktop
• Chrome Mobile
• Safari Mobile

Screen readers

I tested the build on the following browsers:

• JAWS Firefox Desktop
• JAWS Chrome Desktop
• NVDA Firefox Desktop
• NVDA Chrome Desktop
• VoiceOver Safari Desktop
• VoiceOver Chrome Desktop
• VoiceOver Safari Mobile
• Android Accessibility Suite Chrome Mobile

Pull request type

Please check the type of change your PR introduces:

• Bugfix
• Feature
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no api changes)
• Build related changes
• Documentation content changes
• Other (please describe):

Does this introduce a breaking change?

• Yes
• No

Other information

[jeripeierSBB]

Very nice cleanup, I like it :)

[kyubisation]

LGTM 👍
Nice work! 😃

[codecov-commenter]

Codecov Report

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