Exclude files from Searches | Mark directories as excluded

**Is your feature request related to a problem? Please describe (REQUIRED):**
When using "Search in Files" or "Open Asset" it often includes files I am not interested in. When I develop I usually have external libraries, test, and other data that I know I don't want to show up in any kind of search.

**Describe the solution you'd like (REQUIRED):**
I would like to be able to mark these directories as excluded to stop them from ending up in any "search" dialog.

**Describe alternatives you've considered (REQUIRED):**
Doing it manually

**Additional context (OPTIONAL):**
Common feature in other IDEAs however there they would also be excluded from any Language Server feature which I don't think I want here.

This is an editor only feature and would infer no change on any builds.