Highlight all occurrences of selection (like in VSCode)

### What
The description says it all - select some text, then the editor will highlight all other occurrences of the same text.

### Why
Very handy in IDEs, but also when searching for a particlular word in my notes - it's wuickier then ctrl+f, then typing

### How
An example:
https://marketplace.visualstudio.com/items?itemName=wenquansun.Highlightalloccurrencesofselectedword

No file, test, or entry point is named. Start by locating the editor's selection and highlighting behavior in the TypeScript code, then compare the result with the linked VSCode example; done means selecting text highlights all matching occurrences.

Written by the indexing model from the issue text.