Update and consolidate demos into samples

[alschmiedt]

Category Examples

Component All examples

Is your feature request related to a problem? Please describe. We currently have quite a few examples that we have moved over to samples but also left in core. This is pretty annoying when we have to fix a bug for one of them and have to duplicate the bug fix.

Describe the solution you'd like

• [x] Remove duplicate examples/demos.
• [x] Add redirects to the demos page so that they redirect to the appropriate page on samples.
• [ ] Remove any broken/not useful demos/examples.
• [ ] Finish migrating over any examples/demos to samples.

Describe alternatives you've considered

Additional context

[rachel-fenichel]

See also https://github.com/google/blockly/issues/6065

[maribethb]

I think we can close this as the only remaining demos are listed in #6065.