Update Gulp; Remove Yarn; Add Godot icons

[JMS55]

• This project was using an older version of gulp that does not work on newer npm/node versions, I updated it
• I removed Yarn, as npm now has lockfiles
• The Godot icons I added don't fit in super well with this theme's style (espeically .material), but it's better than nothing. If you could create new icons based on these, that would be amazing!
• I didn't add an icon for .tres (text file resources, for instance default_env.tres is a 3D environment description saved to a file), as I was unsure what would fit
• Conventions probably weren't followed, you might want to optimize the svg's / change the filenames
• Changelog/verison info, etc need to be modified still

Closes #14

[JMS55]

Oh, I also forgot to mention

• License for godot icon, may need attribution
• License for other icons added

[vigan-abd]

fyi since repo is no longer active I've created a fork, rewrote the gulp part with latest package versions and also published it:

https://github.com/vigan-abd/studio-icons-v2 https://marketplace.visualstudio.com/items?itemName=vigan-abd.vscode-icon-v2&ssr=false#review-details