feat: add calciteInvalid event for form validation (#9211)

**Related Issue:** #9210

## Summary

Add a `calciteInvalid` event (like
[`invalid`](https://developer.mozilla.org/en-US/docs/Web/API/HTMLInputElement/invalid_event)),
which fires if a component's validation constraints aren't met during
form submission. This will make it easier to set custom validation
messages on form submission. Once #9210 lands, I'll update the new
validation demo it adds to use `calciteInvalid`.

packages/calcite-components/src/tests/commonTests/formAssociated.ts

@@ -167,13 +167,19 @@ export function formAssociated(
 
     const submitButton = await page.find("#submitButton");
     const spyEvent = await page.spyOnEvent(getClearValidationEventName(tag));
+    const spyInvalidEvent = await page.spyOnEvent("calciteInvalid");
 
     const requiredValidationMessage =
       options?.inputType === "radio" ? "Please select one of these options." : "Please fill out this field.";
 
     await assertPreventsFormSubmission(page, component, submitButton, requiredValidationMessage);
+    expect(spyInvalidEvent).toHaveReceivedEventTimes(1);
+
     await assertClearsValidationOnValueChange(page, component, options, spyEvent, tag);
+    expect(spyInvalidEvent).toHaveReceivedEventTimes(1);
+
     await assertUserMessageNotOverridden(page, component, submitButton);
+    expect(spyInvalidEvent).toHaveReceivedEventTimes(2);
   }
 
   function ensureName(html: string, componentTag: string): string {

packages/calcite-components/src/utils/form.tsx

@@ -260,6 +260,9 @@ function invalidHandler(event: Event) {
   // prevent the browser from showing the native validation popover
   event?.preventDefault();
 
+  // dispatch a "calciteInvalid" so users can set custom validation messages
+  formComponent.dispatchEvent(new CustomEvent("calciteInvalid", { bubbles: true, composed: true }));
+
   displayValidationMessage(formComponent, {
     message: hiddenInput?.validationMessage,
     icon: true,