[misc] vim/syntax: Very magic patterns

[misc] vim/syntax: Very magic patterns

From Vim's |pattern.txt|, |/\v| |/\V|:
> Use of "\v" means that after it, all ASCII characters except
> '0'-'9', 'a'-'z', 'A'-'Z' and '_' have special meaning: "very magic"

This mostly makes some upcoming syntax pattern refactoring cleaner,
though most patterns still get shorter here.