Globbing support in :open

[mo8it]

Closes #5706

The functionality is almost done, but I would like to have feedback on how to improve the error handling.

Please tell me if you prefer moving the two inner functions to somewhere else.

Things to discuss:

• Should I ignore directories when globbing? Currently, running something like :open * opens all files in the current directory and multiple file pickers for all directories in the current directory. Update: I ignore directories when globbing now.
• We probably should set an upper limit of paths to open. How should this limit be set? Should it be configurable or just a constant? Currently, it is a constant set to 32.
• Should I add tests for the globing functionality? If yes, where?

[daedroza]

Great functionality, testing here and works good!

[mo8it]

I added an upper limit of files to open with a glob and implemented ignoring directories when globbing. The PR is ready to be merged after a review 😃

[postsolar]

Currently this breaks opening non-existent file, e.g. :o file_which_doesnt_exist.txt.

[mo8it]

@postsolar You are right. I will fix it in the next days.

[mo8it]

Fixed opening non-existent files and merge conflicts.

[mo8it]

I was too focused on skipping non-relevant parents 😅 I just use the parallel ignore walker now. Ready for a review :)