Backport #22864
Collapsing folders currently just throws a console error
```
index.js?v=1.19.0~dev-403-gb6b8feb3d:10 TypeError: this.$set is not a function
at Proxy.handleClick (index.js?v=1.19.0~dev-403-gb6b8feb3d:58:7159)
at index.js?v=1.19.0~dev-403-gb6b8feb3d:58:6466
at index.js?v=1.19.0~dev-403-gb6b8feb3d:10:93922
at ce (index.js?v=1.19.0~dev-403-gb6b8feb3d:10:1472)
at Q (index.js?v=1.19.0~dev-403-gb6b8feb3d:10:1567)
at HTMLDivElement.$e (index.js?v=1.19.0~dev-403-gb6b8feb3d:10:79198)
```
This PR fixes this and allows folders to be collapsed again.
Also:
- better cursor interaction with folders
- added some color to the diff detail stats
- remove green link color from all the file names
Screenshots:
Co-authored-by: gempir <daniel.pasch.s@gmail.com>
Co-authored-by: zeripath <art27@cantab.net>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
Yarden Shoham
