feat(fish): add support for fish

TODO.rst

@@ -22,7 +22,6 @@ queries.  Contributions are welcome.
 
 - devicetree
 - elm
-- fish
 - gdscript
 - graphql
 - kotlin

queries/fish/rainbow-delimiters.scm

@@ -0,0 +1,15 @@
+(command_substitution
+  "(" @opening
+  ")" @closing) @container
+
+(concatenation
+  "[" @opening
+  "]" @closing) @container
+
+(list_element_access
+  "[" @opening
+  "]" @closing) @container
+
+(brace_expansion
+  "{" @opening
+  "}" @closing) @container

test/highlight/fish/regular.fish

@@ -0,0 +1,7 @@
+set -l shells "$SHELL" /bin/{zsh,bash,sh} (which nu) /usr/bin/xonsh
+
+echo "Your first few shells is $shells[1..3]"
+
+if set -q shells[10]
+    echo "You defined at least 10 shells"
+end