feat: add separate endpoint to fetch function names for autocomplete (#12840)

* WIP

* Add unit test for API

* Add spec

* Fix unit test

* Fix unit test

* Fix test

* Fix test

* Add period to error message

superset-frontend/src/SqlLab/components/AceEditorWrapper.tsx

@@ -41,6 +41,7 @@ type HotKey = {
 interface Props {
   actions: {
     queryEditorSetSelectedText: (edit: any, text: null | string) => void;
+    queryEditorSetFunctionNames: (queryEditor: object, dbId: number) => void;
     addTable: (queryEditor: any, value: any, schema: any) => void;
   };
   autocomplete: boolean;
@@ -85,6 +86,10 @@ class AceEditorWrapper extends React.PureComponent<Props, State> {
   componentDidMount() {
     // Making sure no text is selected from previous mount
     this.props.actions.queryEditorSetSelectedText(this.props.queryEditor, null);
+    this.props.actions.queryEditorSetFunctionNames(
+      this.props.queryEditor,
+      this.props.queryEditor.dbId,
+    );
     this.setAutoCompleter(this.props);
   }
 

superset-frontend/src/SqlLab/components/SqlEditor.jsx

@@ -474,9 +474,7 @@ class SqlEditor extends React.PureComponent {
             sql={this.props.queryEditor.sql}
             schemas={this.props.queryEditor.schemaOptions}
             tables={this.props.queryEditor.tableOptions}
-            functionNames={
-              this.props.database ? this.props.database.function_names : []
-            }
+            functionNames={this.props.queryEditor.functionNames}
             extendedTables={this.props.tables}
             height={`${aceEditorHeight}px`}
             hotkeys={hotkeys}

superset-frontend/src/SqlLab/components/SqlEditorLeftBar.jsx

@@ -80,6 +80,10 @@ export default class SqlEditorLeftBar extends React.PureComponent {
 
   onDbChange(db) {
     this.props.actions.queryEditorSetDb(this.props.queryEditor, db.id);
+    this.props.actions.queryEditorSetFunctionNames(
+      this.props.queryEditor,
+      db.id,
+    );
   }
 
   onTableChange(tableName, schemaName) {