Code coverage

[credondocr]

Check for existing issues

• [X] Completed

Describe the feature

As a Golang developer, I want to show the code coverage inline when a function is covered or missing to be tested, the following image is just to add the expected behavior thinking that exists in Visual Studio code and other modern text editors

Visual Studio

If applicable, add mockups / screenshots to help present your vision of the feature

image from https://marketplace.visualstudio.com/items?itemName=markis.code-coverage

Image from https://marketplace.visualstudio.com/items?itemName=ryanluker.vscode-coverage-gutters

[fmartingr]

Just to add more suggestions, I'd rather go with gutter display rather than line highlight. From VSCode I feel line highlight to be useful for errors/warnings (#4901).