Update documentation to be web/html-first

[mrosvik]

We now have a web package with observers and custom elements to help with interactivity across frameworks. We should update our documentation to provide an agnostic approach first and React second.

[mimarz]

Meeting on 8 april with @mrosvik @eirikbacker @frankdahle @oddvernes

General concensus was that we liked the dropdown format page the best: #4630

To begin with we will focus on the following.

• Keep the three tabs for segregating information - might look at combining into one page in the future.
• HTML/CSS and general code information about the component in the top of code tab.
• Keep livecomponent preview at the top of code tab, but set it be lang="html" as default.
• Everything related to React in a separate chapter at the end of code tab.
• CSS classes and attributes chapter will be before React chapter.
• We will not introduce a global toggle for react/html.
• A lot of documentation needs to be revisied and cleaned up.
• Move most examples to "oversikt", keep only code specific things in "kode" tab.
• Pivot documentation to talk about concept instead of React component. This includes less use of code annotation and names according to React component.
  • For example; "ErrorSummary er en oppsummering av feil" should be rewritten to "Error summary er en oppsumering av feil."
  • ToggleGroup -> Toggle group etc.