Workspace Search: Don't load binary files unless needed

[Wittmaxi]

When performing a workspace Search (Ctrl + H) and excluding search in binary files, we currently still load all files in order to determine which files to look through.

Ideally, we would only look into files which we know to be nonbinary, for example by discriminating based on file-extension.
I am not sure what an ideal solution would look like.

Issue stems from a discussion in #2180

[Wittmaxi]

@christianstaib

[jukzi]

is this (still) an issue? Please either provide a reproducer with measurement (sampling) or close the issue