feat: add visual block-wise mode

[fitrh]

I made this PR because I don't know if the block-wise visual mode (Ctrl+v) was intentionally ignored or forgotten, if it was intentional, feel free to close it.

[fitrh]

It seem github diff does not render the Ctrl+v characters, here's the diff

[mvllow]

Thank you for adding this 😌

Your diff image shows ^V on both line 201 and 206 but copying this locally, I only see ^V on line 206, whereas 201 is an empty string

[fitrh]

Yes, copy-paste from github diff doesn't give correct characters, it should be cloned

[mvllow]

Wish there was a better way to get the ^V modes that rendered properly everywhere – I could see that being confusing for contributors viewing the code on GitHub. I was unable to find any other way though so this is good 💜

[fitrh]

As I can recall, it's something called control character

[fitrh]

Found it, :help i_CTRL-V

[mvllow]

This does seem to work via nvim_replace_termcodes('<C-V>', true, true, true) 🎉