fix: resolve #986 avoid wrong offset on Neovim for some postfix snippets

[Eric-Song-Nop]

resolve #986

According to lsp spec, additional text edit is not supposed to be used here.

/**

• An optional array of additional text edits that are applied when
• selecting this completion. Edits must not overlap (including the same
• insert position) with the main edit nor with themselves.
• Additional text edits should be used to change text unrelated to the
• current cursor position (for example adding an import statement at the
• top of the file if the completion item will insert an unqualified type).
  */

[Eric-Song-Nop]

Other uses of additional_text_edits should also be replaced gradually

[Myriad-Dreamin]

The range of main edit can only start at the cursor, but rng.start is before the cursor.

[Myriad-Dreamin]

Probably not, the lsp spec says, "it must be a [single line] and they must contain the position at which completion has been requested," rather than "start with the position".

[Eric-Song-Nop]

Yes, that's why it is ended in self.from.

[Eric-Song-Nop]

Maybe I should use the insertandreplace capability of lsp

[Myriad-Dreamin]

As the lsp spec said above, rng.start..self.from may span across multiple lines but the spec requires it MUST be in a single line so I don't think this is a valid fix. Btw, I checked it in my local neovim, and at least the case in #986 can work as expected. It might be worth to checking whether some neovim completion plugins don't work while others do work. I use the default LazyVim plus the tinymist.lua from the commit.

[Eric-Song-Nop]

I am not sure if this is a common problem, so I am turning this pr in to a specific one for #986, thus the current implementation should be enough.