Filter Staged/Unstaged files, currently only branches and commits can be filtered

**Is your feature request related to a problem? Please describe.**
When filtering while on the "files" tab, I expected to filter the files, not branches/commits.
I can search using '/', but not filter.
When working on mono repos, this is an essential feature.

**Describe the solution you'd like**
c-s is the default for filtering. If one is on the second tab (Files), when filtering with c-s, hide any other files/folders that don't fit the search. Regex support would also be nice, but a simple text search would go a long way.

**Describe alternatives you've considered**
Simple text filter

**Additional context**
A situation that one has to consider is to perhaps have a visual warning/q if one is committing while it has filtered files, but some other files are staged but not visible due to the filter to avoid committing unwanted files by accident.