Map ignore files to Git Ignore syntax

This would catch any dotfiles that end in "ignore", but not `.ignore`

Set as a lower priority rule (90 vs the usual 50) because it's a blanket
assignation. If there are conflict with other, more specific rules,
those will take precedence.

CHANGELOG.md

@@ -35,6 +35,7 @@
 - Add syntax highlighting support for COBOL, see #3584 (@adukhan99)
 - Fixed manpage syntax so that ANSI escape codes don't get incorrectly highlighted and thus broken, see #3586 (@BlueElectivire)
 - Map several Google Cloud CLI config files to their appropriate syntax #3635 (@victor-gp)
+- Map all ignore dotfiles to Git Ignore syntax #3636 (@victor-gp)
 
 ## Themes
 

src/syntax_mapping/builtins/common/90-ignore-files.toml

@@ -0,0 +1,2 @@
+[mappings]
+"Git Ignore" = [".?*ignore"]