refactor(ui-library): change theming approach

[ChristianHoffmannS2]

What is included

• New css helpers to produce static styles from themed token sets (ThemeIterator)
• Removal of the old renderThemedCssStrings function
• A refactor of all existing css definitions to use the new iterator approach
• Removal of most dynamically inserted style tags in favor of lit's static style class field. See: lit docs

What is not included

• Code generation to automatically include any new themes defined in tokens studio. Theme names and theme inclusion are hard coded at the moment and need to be changed manually.

Hints for reviewers

All changes are of similar nature. So it's not necessary to check each file meticulously. Reviewers should focus on finding visual deviations in Storybook when compared to the develop branch.

Systematic changes for each component:

• CSS definitions now always include all styles for all themes. This is facilitated through the use of the new ComponentThemeIterator / SemanticThemeIterator functions.
• Removal of most dynamically inserted style tags in favor of lit's static style class field. See: lit docs. Exceptions are:
  • form-labels due to missing ShadowRoot
  • range-slider background gradient generation due to dynamic numerical calculations
• CSS selectors are repeated per iterator type (up to three times, once for: base styles without token values, semantic token iterator, component token iterator). This is to be expected.

Issues found during review (Please add your findings here)

• radio-group layout is broken

Closes #740

was just a test