Add syntax highlight code for ignore files

[taconi]

Adding ignore file support by default so you don't need to install the language-ignore plugin.

[Andriamanitra]

I like the idea but I would reconsider the syntax groups. The current colors seem a bit weird because files are not statements, wildcards are not identifiers, and negated files are definitely not errors.

Screenshots

Using the default config:

Using my current config:

Maybe using diff-added and diff-deleted colors would make more sense?

[taconi]

[...] files are not statements, wildcards are not identifiers, and negated files are definitely not errors. Maybe using diff-added and diff-deleted colors would make more sense?

The relationship was based on colors because of the existing identifiers I did not find any related to the ignore file patterns. diff-added and diff-deleted are also not nominally related. I believe one thing that might bother you is that some color schemes add a background color to the error handler, so I don't see any problem with switching to diff-deleted.

[taconi]

If you commit the changes from #3104 (comment) it looks good to me

@Andriamanitra Applied