Support VS Code's foldable `#region` by adding `folding.markers` to `language-configuration.json`

[sohang3112]

Is your feature request related to a problem? Please describe.

In other languages like Python, putting #region and #endregion blocks in code results in VS Code's native foldable regions - that is, the code enclosed in the region can be collapsed (folded / hidden).

Describe the solution you'd like

Add folding.markers to langauge-configuration.json, as shown in VS Code docs: https://code.visualstudio.com/api/language-extensions/language-configuration-guide#folding