complete/fish: Take RIPGREP_CONFIG_PATH into account

The fish completions now also pay attention to the configuration file
to determine whether to suggest negation options and not just to the
current command line.

This doesn't cover all edge cases. For example the config file is
cached, and so changes may not take effect until the next shell
session. But the cases it doesn't cover are hopefully very rare.

Closes #2708

CHANGELOG.md

@@ -2,6 +2,11 @@ TBD
 ===
 Unreleased changes. Release notes have not yet been written.
 
+Feature enhancements:
+
+* [FEATURE #2708](https://github.com/BurntSushi/ripgrep/pull/2708):
+  Completions for the fish shell take ripgrep's config file into account.
+
 
 14.1.1 (2024-09-08)
 ===================