Added support for drag and drop (files and text)

[Amjad50]

This commit tries to replicate how GVim handles drop events for files and text.

added:

• When text is dropped, it will pasted to the current buffer and cursor (nvim_paste).
• When files are dropped when cmdline is closed, they will be opened using :edit or :split (split if the current buffer is modified).
• When files are dropped when cmdline is opened, the names will be added into the cmdline buffer

Note: not sure why Cargo.lock changed to much, only added urlencoding. Its just that the checksum values changed place.

What do you think @vhakulinen ?

[vhakulinen]

Hi. I'm a bit busy with life atm and don't have the time/energy to work on gnvim currently. Drag & drop is definitely a feature that gnvim should have and I really appreciate the work you've done here. But this will have to wait from my site for a while.

Again, I really appreciate the work you've done here.

[fidelski]

Is there any plan to work on this? I would appreciate this feature very much.

[vhakulinen]

Deprecated.

Gnvim was rewritten from ground up for gtk4.