fix: deprecated code, wrong annotations

[DrKJeff16]

Description

Throughout the codebase there have been lots of deprecated code used. Some examples include:

• vim.validate(): Reported here and in vim.validate is deprecated. Feature will be removed in Nvim 1.0 #3499
• vim.loop: We have vim.uv
• nvim_win_set_option() / nvim_buf_set_option(): Replaced by nvim_set_option_value()
• nvim_buf_add_highlight(): Replaced by vim.hl.range()
• nvim_err_writeln(): Replaced by nvim_echo() (according to the Neovim Deprecated docs

I have updated the deprecated code and, for vim.validate() and vim.loop I have set them as fallback depending
on either version or availability, respectively.

Fixes this r/neovim report and #3499.

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• This change requires a documentation update

How Has This Been Tested?

I have ran make test with no failures nor warnings.

Configuration: DrKJeff16/Jnvim

• Neovim version (nvim --version): NVIM v0.12.0-dev-1365+gb938638d2d
• Operating system and version: Arch Linux, Linux 6.16.10-arch1-1

Checklist:

• My code follows the style guidelines of this project (stylua)
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation (lua annotations)

[DrKJeff16]

Note

This is an extended list of fixes offered originally in #3502.