Allow max number of files seen by file_picker to be configurable

[nstinus]

Fixes #5157.
Follow up on #5165.

[David-Else]

Would it be a good idea to warn the user that the max number of files limit had been reached? Otherwise they might be looking for a file that exists that Helix would be hiding from them due to the max-files limit.

At the moment the file picker opens with 100000/100000 displayed when the limit is reached, but that does not really draw attention to the limit. One of the following options could improve things:

1. The /max-files part could be highlighted when reached in the warning colour to draw attention, 100000/100000 <- in red/warning colour
2. A string saying < max files limit reached could be appended, 100000/100000 < max files limit reached

[nstinus]

I think both remarks make sense.

I am also not convinced at the current state of affairs: why would a git tracked repo have no limit when a plain one has this arbitrary value. Surely, if there are too many files, the fact that we are in a git repo is irrelevant. Also, the issue with this approach is that I'd rather have a slow file_picker than not finding the file I am looking for...

Perhaps an alternative could be to get rid of this value altogether and if the file_picker becomes slow, warn the user that there are a lot of files and it may be slow to use?

[nstinus]

@kirawi any thoughts on this ^

[pascalkuthe]

This was adreased by #7814, there is no limit anymore, files are streamed into the picker in the background now (and the matcher is fast enough to handle millions of files).