Added API to configure the filtering debounce timeout

vaadin-combo-box-flow-parent/vaadin-combo-box-flow/src/main/java/com/vaadin/flow/component/combobox/ComboBox.java

@@ -450,4 +450,17 @@ public ComboBoxI18n setRequiredErrorMessage(String errorMessage) {
             return this;
         }
     }
+
+    /**
+     * Sets the "debounce timeout" that the component waits for a short pause in
+     * typing, before triggering a server-side visit to filter items. The
+     * default is 500ms.
+     *
+     * @param filterTimeout
+     *            the time in milliseconds that needs to happen between
+     *            keystrokes until filtering is triggered.
+     */
+    public void setFilterTimeout(int filterTimeout) {
+        getElement().setProperty("filterDebouncerTimer", filterTimeout + "");
+    }
 }

vaadin-combo-box-flow-parent/vaadin-combo-box-flow/src/main/resources/META-INF/resources/frontend/comboBoxConnector.js

@@ -89,7 +89,11 @@ window.Vaadin.Flow.comboBoxConnector.initLazy = (comboBox) => {
     if (filterChanged) {
       cache = {};
       lastFilter = params.filter;
-      this._filterDebouncer = Debouncer.debounce(this._filterDebouncer, timeOut.after(500), () => {
+      let timerValue = 500;
+      if (comboBox.filterDebouncerTimer) {
+        timerValue = comboBox.filterDebouncerTimer;
+      }
+      this._filterDebouncer = Debouncer.debounce(this._filterDebouncer, timeOut.after(timerValue), () => {
         if (serverFacade.getLastFilterSentToServer() === params.filter) {
           // Fixes the case when the filter changes
           // to something else and back to the original value