Custom expression editor: don't clobber SQL editor (#19448)

frontend/src/metabase/query_builder/components/expressions/expressions.css

-.ace_content * {
+.expression-editor-textfield .ace_content * {
   font-family: monospace !important;
 }
 
@@ -20,10 +20,10 @@
   color: var(--color-accent5);
 }
 
-.ace_cursor {
+.expression-editor-textfield .ace_cursor {
   border-left-width: 1px;
 }
 
-.ace_hidden-cursors .ace_cursor {
+.expression-editor-textfield .ace_hidden-cursors .ace_cursor {
   opacity: 0;
 }