Add TypeScript Definitions

[shartte]

Additional notes:

• Pre-commit hooks fail on Windows with issues related to Markdown, although this change includes no Markdown changes.

assets/icons/README.md:3:501 MD013/line-length Line length [Expected: 500; Actual: 533]
README.md:65:53 MD026/no-trailing-punctuation Trailing punctuation in heading [Punctuation: ' !!!']
ERROR: "lint:markdownlint" exited with 1.

• The package.json currently lists build.js as it's entrypoint but that seems incorrect. It should probably be tokens.js to enable importing the tokens directly from @db-ui/base. (also: set module: true)

[mfranzke]

@shartte thanks a lot for your contribution. I've added issues and PRs for the markdownlint problem in parallel.