Docs: remove CodeSandbox embedded demos and add links to working exa,ples in Stackblitz

[sequba]

Context

Codesandbox embedded demos were buggy and of poor developer experience. I changed them to simple links to Stackblitz demos.

Affected demos:

• https://hyperformula.handsontable.com/guide/integration-with-react.html#demo
• https://hyperformula.handsontable.com/guide/integration-with-vue.html#demo
• https://hyperformula.handsontable.com/guide/integration-with-angular.html#demo
• https://hyperformula.handsontable.com/guide/integration-with-svelte.html#demo
• https://hyperformula.handsontable.com/guide/custom-functions.html#working-demo

How did you test your changes?

• local docs build
• tested on staging

Types of changes

• Breaking change (a fix or a feature because of which an existing functionality doesn't work as expected anymore)
• New feature or improvement (a non-breaking change that adds functionality)
• Bug fix (a non-breaking change that fixes an issue)
• Additional language file, or a change to an existing language file (translations)
• Change to the documentation

Related issues:

Fixes #1561
ClickUp issue: https://app.clickup.com/t/9015210959/HF-73

[qunabu]

Task linked: HF-73 Docs demos: Stackblitz link instead of Codesandbox embed