fix(blockwise-visual): handle double-width chars and tabs

[xiyaowong]

improvement: the selection direction is consistent with nvim

Issue - Fixed

[trkoch]

@xiyaowong Not sure I can follow the GIF. The issue you're fixing is that some characters are not selected which should? I merged the PR in my build and will report regressions, if any.

[theol0403]

Isn't there a built in vim function to convert display col to col? Could this PR not be simplified to just converting the column before sending it to VS code? This code seems a little complex.

[xiyaowong]

Isn't there a built in vim function to convert display col to col?

Oh! I forgot to search for the built-in function. There is virtcol2col

[xiyaowong]

@theol0403 Not sure if virtcol2col can simplify the code, after all, we still need to convert byte-index to char-index. And this function depends on a window

[theol0403]

Isn't there also a function to convert char to byte char?

[xiyaowong]

vim.str_utfindex

I'll refactor it when I have time.😪

[theol0403]

What about https://neovim.io/doc/user/builtin.html#charidx()

[xiyaowong]

It seems almost the same

vim.str_utfindex is widely used in nvim-lsp. Maybe it's better?. I'm not sure. I haven't used any of these functions.