sh-script.el: Improve consistency in variable-use fontification.

sh-mode--treesit-settings: Ensure all variable use is treated the
same way.
Before this patch the following commands would all be treated differently:

    echo "${var}"
    echo "$var"
    echo ${var}
    echo $var

Now they are treated the same.
* lisp/progmodes/sh-script.el (sh-mode--treesit-settings): Tweak
rules.  (Bug#78167)

1 files changed, 5 insertions, 1 deletions

diff --git a/lisp/progmodes/sh-script.el b/lisp/progmodes/sh-script.el
index 7216975ebfd..5075e9a0afc 100644
--- a/lisp/progmodes/sh-script.el
+++ b/lisp/progmodes/sh-script.el
@@ -3369,7 +3369,11 @@ See `sh-mode--treesit-other-keywords' and
    :language 'bash
    :override t
    '((command_substitution) @sh-quoted-exec
-     (string (expansion (variable_name) @font-lock-variable-use-face)))
+     (expansion (variable_name) @font-lock-variable-use-face)
+     (expansion ["${" "}"] @font-lock-bracket-face)
+     (simple_expansion
+      "$" @font-lock-bracket-face
+      (variable_name) @font-lock-variable-use-face))
 
    :feature 'heredoc
    :language 'bash