Fix/styles and types cleanup

[aappoalander]

Description

This maintenance PR removes redundant abstractions and typings and simplifies styles handling. Theme handling is refactored to use a provider pattern instead of constant theme. In additions, some minor improvements to folder structure are introduced.

All snapshots remain unchanged.

Motivation and Context

Current styles and types implementations date back over two years to situation where the goal was to have an unstyled abstraction of all components. This is no longer the goal and most of these abstractions have become redundant.

To simplify the codebase, the theme and tokens handling had to be refactored. Theme is now provided via context and can be customized when needed. Components only use the theme via the context and do not import anything else from the theme directly. Theme utils are still used directly, but style related common tools are now located under utils.

In addition, css-in-to-js had multiple vulnerabilities due to no updates and was removed as inspired by PR:#489

Removing of custom Reach-UI typings resulted in simplified implementation of LanguageMenu, which no longer supports custom components or menu popover class names.

How Has This Been Tested?

Tested on MacOS using Chrome, Edge and Safari with VoiceOver. Tested using styleguidist build, CRA-TS and SSR test applications via verdaccio. In addition, tested with styleguidist using Android and Chrome.

Release notes

Theme and styles:

• Add export for suomifiTheme and related interfaces
• Add and export SuomifiThemeProvider and related documentation
• Remove css.in-to-js dependency and replace it with static object
• Refactor theme generation and remove redundant focus utils. Include derived tokens to theme.
  Directory structure:
• Remove unused login icon and directory
• Move styleguidist components to docs directory
• Cleanup utils directory structure
  Types:
• Remove all custom Reach-UI types and replace with the ones exported by Reach-UI
  LanguageMenu:
• Breaking changes: Remove languageMenuPopoverProps and languageMenuPopoverComponent from LanguageMenuProps, remove related interfaces, remove popover and popoverLang classNames from internal styles.

[ketsappi]

Remembered the old issue #225 that can be closed when this PR is ready.

[ketsappi]

Left some comments here and there but none shouldn't be any real problem. Suggestions here and there to open discussion.

Will next test library with test benches.

[ketsappi]

Seems to work nicely when smoke tested in CRA-TS and next.js projects.

Good work!

[LJKaski]

A lot of changes for sure, but seems to work as advertised. Good work :)