feat: add highlighting of selected region

[stevanmilic]

Regression Test

Platforms

• windows
• macOS
• linux

Tasks

• Use <leader>gl to copy git link.
• Use <leader>gL to open git link in browser.
• Copy git link in a symlink directory of git repo.
• Copy git link in an un-pushed git branch, and receive an expected error.
• Copy git link in a pushed git branch but edited file, and receive a warning says the git link could be wrong.

[stevanmilic]

@linrongbin16 I've ported ruifm/gitlinker.nvim#61. lmk if there's anything else to do

[codecov]

Codecov Report

Attention: 16 lines in your changes are missing coverage. Please review.

Files	Coverage Δ
lua/gitlinker.lua	59.52% <62.50%> (-7.59%)	⬇️
lua/gitlinker/highlight.lua	13.33% <13.33%> (ø)

... and 3 files with indirect coverage changes

📢 Thoughts on this report? Let us know!

[linrongbin16]

i am not in front of my keyboard, will test later

[linrongbin16]

test good, merged into master. hi @stevanmilic , really thanks to your PR!