[Feat] Suport `.gitignore` and `.eslintignore` files to populate ignore list

[phoenisx]

cssvar.ignore can be tedious to maintain, and ignore list can be random for different projects. Adding support for .gitignore and .eslintignore files opens an opportunity to keep less things inside the extension config and re-use config files that are widely used.

Gotchas:

• If a folder (like node_modules) is ignored in .gitignore and later user wants to import a css file from node_modules, the extension should not ignore such CSS imports from node_modules.
  • I guess this should be possible using !node_modules glob pattern in cssvar.ignore settings, which will supersede all other ignore patterns.

[phoenisx]

This issue will only support .gitignore files.

Support for .eslintignore can be added on demand later, if ever needed.

[phoenisx]

I will wait to work on this. I think creating a small library to provide this functionality and also support glob patterns would be an interesting project to work on. 😅